Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

IntroductionA greenhouse is a controllable dynamic system (Seginer 1996), managed for intensive production

of high quality, fresh market produce. Greenhouse production allows for crop production under

very diverse conditions (Gauthier 1992). However, there are a number of variables that

greenhouse growers have to manage in order to obtain maximum sustainable production from

their crops. These variables include; air temperature, root zone temperature, vapour pressure

deficit, fertilizer feed, carbon dioxide enrichment, selection of growing media, and plant

maintenance. The task of managing these inter-related variables simultaneously can appear

overwhelming, however, there are successful strategies that are used by growers to do this. The

main approach is to try to optimize these variables to obtain maximum performance from the

crop over the production season.

The goal of optimization can be used to determine how to control these variables in the greenhouse for maximum yield and profit, taking into account the costs of operation and increased value under the modified environment (Jones et al 1991). The greenhouse system is complex; to simplify the decision-making process growers use indicators. An indicator can be thought of as a small window to a bigger world, you don't get the entire picture, but you do gain an understanding of what is happening. Another way to look at it is to understand the basic rules of thumb which can be used to obtain insights on the direction and dynamics of the crop-environment interaction. Indicators provide information concerning complex systems in order to make them more easily understandable (Giradin et al 1999). They quickly reveal changes in the greenhouse which may require alterations in management strategies. Indicators also help identify the specific changes in crop management that need to be made. The purpose of this manual is to provide information regarding the greenhouse management, and the resultant response of the sweet bell pepper plant as individuals within the larger crop. Basic indicators used to evaluate the plant-environment interaction to move towards optimization of the environment and crop performance are presented. Over time, and with experience, growers will be able to build on

these basic indicators to improve their ability to respond to changes in the crop and to anticipate the needs of the crop.

Important

This guide is intended for commercial growers in Alberta, and is based on the most recent recommendations for greenhouse sweet pepper production. As each greenhouse is unique, growers should adapt the information to their operations. Specific climate recommendations are to be used only as a guide.

Acknowledgements Sweet bell peppers Concepts involved in the optimization of the greenhouse environment for crop

production Components of the greenhouse system for environmental control

The greenhouse structure The header house The plant nursery

Providing heat Providing heat to the air, the plant canopy Providing heat to the root zone Providing heat to the heads of the plants

Ventilation and air circulation Ventilation systems Air circulation, horizontal air flow (HAF) fans

Cooling and humidification Pad and fan evaporative cooling Mist systems

Greenhouse floors Carbon dioxide supplementation

Carbon dioxide supplementation via combustion Natural gas CO2 generators Boiler stack recovery systems

Liquid CO2 supplementation Irrigation and fertilizer feed systems Computerized environmental control systems

Management of the greenhouse environment Light

Properties of light and its measurement The light use efficiency of plants Maximizing the crop's access to available light

Temperature management Managing air temperatures

Precision heat in the canopy Managing root zone temperatures

Management of relative humidity using vapour pressure deficits Carbon dioxide supplementation

Air pollution in the greenhouse Growing media

Media for seeding and propagation Growing media for the production greenhouse

Management of irrigation and fertilizer feed Water quality

Electrical conductivity of water pH

The mineral nutrition of plants Fertilizer feed programs

Designing a fertilizer feed program Accounting for the nutrients present in the raw water Accounting for the nutrients provided by the pH adjustment of the

water Determining the required amounts of the various fertilizers

necessary to meet the feed targets Rules for mixing fertilizers Application of fertilizer and water

Production of sweet bell peppers Introduction Cultivars Pepper plant propagation

Seeding First transplanting: Into the rockwool blocks Growing media in the production greenhouse Planting density Transplanting into the production greenhouse "house-set" Pruning and plant training Flower and fruit set Irrigation Harvesting and grading Greenhouse production costs and returns for peppers The Zen of Greenhouse Peppers

End of season cleanup Steam sterilization of rockwool slabs

Pest and disease management Crop monitoring Cultural control Resistant cultivars Biological control Chemical control

Pests of greenhouse sweet peppers and their biological control Assessment of the quality of biological control agents Aphids Two-spotted spider mite Thrips Loopers and caterpillars

Whitefly Fungus gnats Lygus bugs Earwigs

Diseases of sweet pepper Fungal diseases

Damping-off Pythium crown and root rot Fusarium stem and fruit rot Gray mold Powdery mildew

Virus diseases Pepper mild mottle virus Tobacco mosaic virus Tomato spotted wilt virus Tomato mosaic virus

Physiological Disorders Blossom end rot Sunscald Fruit cracks Fruit splitting Fruit spots Misshapen fruit Internal growths in the fruit

Appendices Appendix I. Effect of Pesticides on Biological Control Agents* Appendix II. Plant nutrient deficiency symptoms

Bibliography

This information is maintained by James Calpas Last Revised/Reviewed March 7, 2001

Sweet Bell Peppers

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Bell peppers (Capsicum annum L.) originate from central and south America where numerous species were used centuries before Columbus landed on the continent (Manrique 1993). The cultivation of peppers spread throughout Europe and Asia after the 1500's. Although perennials, they grow as annuals in temperate climates. They are sensitive to low temperatures and are relatively slow to establish. As there is little field production of bell peppers in Alberta, greenhouse production provides most of the local source of this product. Greenhouse production of peppers is based on indeterminate cultivars in which the plants continually develop and grow from new meristems that produce new stems, leaves, flowers and fruit. In comparison, field pepper cultivars are determinate, the plant grows to a certain size, produces fruit and stops growing and eventually dies. Indeterminate cultivars require constant pruning to manage their growth. In order to optimize yield, a balance between vegetative (leaves and stems) and generative (flowers and fruit) growth must be established and maintained.

Figure 1. Canopy of a healthy greenhouse sweet bell pepper crop. Greenhouse pepper production is based on a year long production cycle. Typically, seeding occurs in early to mid October, plants are moved from the nursery into the production greenhouses six weeks later, just before Christmas. Harvest begins in late March and continues through to the following November. It takes roughly four months from seeding to first pick.

Figure 2. Basket of red sweet bell peppers ready for market.

Concepts Involved in the Optimization of the Greenhouse Environment for Crop Production

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Greenhouse vegetable crop production is based on control of the environment in such a way as to provide the conditions that are most favorable for maximum yield. A plant's ability to grow and develop is dependent on the photosynthetic process. In the presence of light, the plant combines carbon dioxide and water to form sugars which are then utilized for growth and fruit production. Photosynthesis is practically the only mechanism of energy input into the living world (Salisbury and Ross, 1978). Optimization of the greenhouse environment is directed at optimizing the photosynthetic process in the plants, the plant's ability to utilize light at maximum efficiency. Tied closely to the photosynthetic process is the process of transpiration. Transpiration can be defined as the evaporation of water from plants (Salisbury and Ross 1978). Transpiration occurs through pores in the leaf surface called stomata (Salisbury and Ross 1978, Papadakis et al 1994). As water is lost from the leaf, a pressure is built up that drives the roots to find additional water to compensate for the loss. The evaporation of the water from the leaf serves to cool the leaf ensuring that optimum leaf temperatures are maintained. As the roots bring additional water into the plant, they also bring in nutrients which are sent throughout the rest of the plant with the water. Water is a key component of photosynthesis, as is carbon dioxide (CO2) which is often the limiting component of the process. The plant's source of carbon dioxide is the atmosphere as carbon dioxide exists as a gas at

temperatures in the growing environment. Carbon dioxide enters the plant through the stomata in the leaves, and this is where it can be seen why transpiration represents a compromise to photosynthesis for the plant.

Figure 3. Cross section of a leaf showing stomata. Plants have control over whether the stomata are open or closed. They are closed at night and open in response to the increasing light intensity that comes with the morning sun. The plant begins to photosynthesize and the stomata open in order to allow more carbon dioxide into the leaf. As light intensity increases, so does leaf temperature, and water vapour is lost from the leaf which serves to cool the leaf. The compromise with photosynthesis occurs when the heat stress in the environment causes such a loss of water vapour through the stomata that the movement of carbon dioxide into the leaf is reduced. The other factor involved with this process is the relative humidity in the environment. The transpiration stress on a leaf, and the plant at any given temperature, is greater at a lower relative humidity than a higher relative humidity. There also comes a point where the transpiration stress on the plant is so great that the stomata close and photosynthesis stops completely. Photosynthesis

6 CO2 + 12 HO - Light energy -> C6H12O2 + 6 O2 + 6 H2O Photosynthesis is the plant process by which carbon dioxide and water with the input of light energy yields sugars, oxygen and water. Photosynthesis is one of the most significant life processes, all the organic matter in living things comes

Respiration is another process tied closely to photosynthesis. All living cells respire continuously (Salisbury and Ross 1978), and the overall process involves the breakdown of sugars within the cells, resulting in the release of energy which is then used for growth (Wilson and Loomis 1967, Salisbury and Ross 1978, Tootil and Blackmore 1984). Through photosynthesis plants utilize light energy to form sugars, which are then broken down by the respiration process, releasing the energy required by plant cells for growth and development.

Photosynthesis responds instantaneously to

about through photosynthesis. The above formula is not quite complete, as photosynthesis will only take place in the presence of chlorophyll, certain enzymes and cofactors. Without discussing all these requirements in detail, let it be enough to say that these cofactors, enzymes, and chlorophyll will be present if the plant receives adequate nutrition. One other point to clarify is that it takes 673,000 calories of light energy to drive the equation (Wilsone and Loomis, 1967). Photosynthesis requires certain inputs to get the desired outputs. Carbon dioxide and water are combined and modified to produce sugar. The sugars are further used to form more complex carbohydrates and oils and so on. Running along side of the photosynthetic process are many more processes in the plant which help ensure that the plant does whit it is designed for. From the grower's point of view, the results of photosynthesis is the production of fruit. This serves to remind that the management decisions made in growing crops affect the outcome of how well the plant is able to run its photosynthetic engines to manufacture those products which are shipped to market. Growers provide the nutrition

changes in light (Seginer 1996) as light energy is the driving force behind the process (Salisbury and Ross 1978). Generally, light is a given, with greenhouse growers relying on natural light to grow their crops. Optimization of photosynthesis can occur through providing supplemental lighting when natural light is limiting. This strategy is not common with the economics involved in supplemental lighting being the determining factor. The common strategy for optimizing photosynthesis comes about through optimizing transpiration. If, under any given level of light, transpiration is optimized such that the maximum amount of carbon dioxide is able to enter the stomata, then photosynthesis is also optimized. The benefit of optimizing photosynthesis through controlling transpiration is that the optimization can occur over both low and high light levels, although photosynthesis is naturally lower under lower light levels. Supplemental lighting is only useful in optimizing photosynthesis at low light levels.

Inherent to high yielding greenhouse crop production are the concepts of plant balance and directed growth. A plant that is growing in the optimum environment for maximum photosynthetic efficiency may not be allocating the resultant production of sugars and starches for maximum fruit production. Greenhouse vegetable plants respond to a number of environmental triggers or cues, and can alter their growth habits as a result. The simplest example is whether they have a vegetative focus or a generative focus. A plant with a vegetative focus is primarily growing roots, stems and leaves, a plant with a generative focus is concentrating on flowers and fruit production. Vegetative and generative plant growth can be thought of two ends of a continuum, the point where maximum sustained fruit production takes place is where vegetative growth is

and environment which direct the plant to optimize photosynthesis and fruit development. Crop management decisions require a knowledge of how to keep the plants in balance so that yield and productive life of the crop is maximized. balanced with generative growth. Complete optimization of the growing environment for crop production also includes providing the correct environmental cues to direct the growth of plants to maintain a plant balance for profitable production. The critical environmental parameters affecting plant growth that growers can control in the greenhouse are temperature, relative humidity, carbon dioxide, nutrition, availability of water, and the growing media. The way environment affects plant growth is not necessarily straightforward and the effect of one parameter is moderated by the others (Stanghellini and Van Meurs 1992). The presence of the crop canopy also exerts considerable influence on the greenhouse environment (Hanan 1990). The ability of growers to provide the optimal environment for their crops improves over time with experience. There is a conviction that environmental control of greenhouses is an art which expert growers bring to perfection (Seginer 1996). This being said, there are basic rules, and environmental setpoints that beginner growers can follow as a blueprint to grow a successful crop. As the plants develop from the seedling phase to maturity, the conditions which determine the optimum environment for the crop also change (Seginer and McClendon 1992). Further, even when the crop is into full production, modifications of the environment may be necessary to ensure that maximum production is maintained. For example, the plants may start to move out-of-balance to become too vegetative or too generative. Through all stages of the crop cycle, growers must train themselves to recognize the indicators displayed by the crop to determine what adjustments in the environment are necessary, if any.

Components of the Greenhouse System for Environmental ControlIntroduction

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Greenhouse production is a year round proposition. In Alberta this means providing an optimal indoor growing environment when the outside environment can be warmer and drier, or colder than what the crop plants require, and in the case of our winters, can even survive. Periods during the winters can drop to - 30 to - 40 °C, the temperature differential between the greenhouse environment and the outdoors can range from 50 to 60 °C . Conversely, during the summers the outdoor temperatures can rise to +35 °C under the intense Alberta sunlight; this is especially true in southern Alberta . Greenhouse temperatures rise under intense sunlight. This rise in temperature is referred to as "solar gain". To enter the greenhouse, light has to travel through the greenhouse covering, in doing so the light loses some of its energy which is converted to heat. Without a cooling system, the temperature within the greenhouse can rise to over + 45 °C. To successfully optimize the environment within the greenhouse means countering the adverse effects of the external environment as it varies over the normal seasons of the year. The effectiveness of greenhouses to allow for environmental control is dependent on the component parts. This section describes the component parts of a typical Alberta vegetable production greenhouse, recognizing that specific systems for environmental control can vary and change from one greenhouse to the next as well as over time as new technology is developed and commercialized. There are basic requirements for environmental control that all greenhouses must meet to be able to produce a successful crop. The simplest example is that a structure is required. Beyond this, there are a number of options that can be included. The most precise control of an environment invariably comes with the inclusion of more technology and equipment and the associated higher cost. The driving force for inclusion of newer or more complex systems is the effect on the financial bottom line and the availability of capital.

The Greenhouse Structure

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Figure 4. Typical gutter connect, doubly poly, vegetable production greenhouse. The greenhouse structure represents both the barrier to direct contact to the external environment and the containment of the internal environment to be controlled. The covering material by design allows for maximum light penetration for growing crops. There are a number of commercial greenhouse manufacturers and a number of greenhouse designs that are suitable for greenhouse vegetable crop production. The basic greenhouse design use for pepper production and vegetable production in general is a gutter connect greenhouse. A gutter connect greenhouse by design allows for relatively easy expansion of the greenhouse when additions are planned. Gutter connect greenhouses are composed of a number of "bays" or compartments running side by side

along the length of the greenhouse. Typically these compartments are approximately 37 meters (120 feet) long by 6.5 to 7.5 meters ( 21 to 25 feet) wide. The production area is completely open between the bays inside the greenhouse, the roof of the entire structure consists of a number of arches, with each arch covering one bay, the arches are connected at the gutters where one bay meets the next. The design of a gutter connect greenhouse allows for a single bay greenhouse of 240 m² (2,500 ft.²) to easily expand by the addition of more bays, to cover an area of a hectare (2.5 acres) or more. With a gutter connect greenhouse, the lowest part of the roof are the gutters, the points where the adjacent arches begin and end. The trend for gutter heights in modern greenhouses is to increase, with greenhouses getting taller. The reason for this is two-fold; firstly, newer vegetable crops like peppers have a requirement for a higher growing environment. Peppers will often reach 3.5 meters (12 feet) in height during the course of the production cycle. Taller greenhouses allow for more options in crop handling and training. Secondly, taller greenhouses allow for a larger air mass to be contained within the structure, and a larger air mass is relatively easier to control with respect to maintaining an optimum environment than a smaller air mass per unit growing area of greenhouse. The reason for this is, the greenhouse environment has inertia (Seginer 1996), once a grower has established an environment in the air mass, it is easier to maintain the environment. Typical gutter heights for modern greenhouse structures are 4 to 4.25 meters (13 to 14 feet), and are quite suitable for greenhouse pepper production. The trend for future gutter height is to increase further, with new construction designs moving to 4.9 to 5.5 meters ( 16 to 18 feet) (Khosla S. 1999).

Figure 5. New greenhouse under construction. There are a number of options for greenhouse covering materials, glass panels, polycarbonate panels, and polyethylene skins are the prevalent choices in Alberta. Each of the coverings have advantages and disadvantages, the main determining factors usually being the trade-off between cost and length of service. Glass is more expensive, but will generally have a longer service life than either polycarbonate or

polyethylene. Typical Alberta vegetable production greenhouses are constructed with double polyethylene skins. Two layers of polyethylene, with pressurized air filling the space between the two layers to provide the rigidity to the covering. The life expectance of a polyethylene greenhouse covering is about 4 years. Energy conservation is also important, the ability of the covering to allow light into the greenhouse and yet reduce the heat loss from the greenhouse to the environment during the winter. New coverings are being developed which selectively exclude certain wavelengths of light and as a result can help in reducing insect and disease problems (pers comm Dr. M. Mirza).

The Header House

The header house is an important component of the greenhouse design. The header house serves as a loading dock where produce is shipped and supplies are received. It also serves to house the nerve center of the environmental control system as well as housing boilers and the irrigation and fertilizer tanks. The header house is kept separate from the main greenhouse with access gained through doors. Lunchroom and washroom facilities are also located in the header house. These facilities should be placed so that they satisfy all food safety requirements with respect to the handling of produce.

The Plant Nursery

The greenhouse design can also include a plant nursery for those vegetable growers who are interested in starting their own plants from seed. The alternative is to contract another greenhouse to grow and deliver young plants ready to go into the main production area. Pepper plants are transplanted in the main greenhouse at about six weeks of age. Growers starting their plants from seed have to have a nursery area in which to do this. It is important to have a nursery of adequate size to supply enough transplants for the entire area of the production greenhouse. Generally speaking, the nursery area is built to obtain a higher degree of specific control than the main production area of the greenhouse as young plants are more sensitive to the environment. The nursery area can be used for production once the seedlings have been moved out. Heated benches or floors are a must as is supplemental lighting. The requirements for pepper seedling production is discussed in detail in "Pepper plant propagation" section

Providing Heat

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

An adequately sized heating system is a must for greenhouse production in Alberta. The output of the system must be able to maintain optimal temperatures on the coldest days of the year. Beyond

the actual sizing of the system, and deciding what form of heating to use, ie. forced air, boiler heat, or both there are special considerations in where the heat is applied, specifically heat applied to the air directed at influencing the plant canopy, and heat applied to the floor to influence the root system. The basic premise behind this concept is that it is difficult to provide optimum root zone temperatures during the cold period of the year by only heating the air. Besides the difficulty in driving warm air down to the greenhouse floor, there is also the associated problem of having to provide too much heat to the canopy in order to try to optimize root zone temperatures. Conversely, floor heat, ie. hot water, steam, oil or glycol systems can easily be used to maintain root zone temperatures, they cannot be used to optimize air temperatures without providing excessive root temperatures. It is also important to note that heating systems, in addition to providing the optimum temperatures for crop growth and yield, also can be employed in combination with controlled venting to dehumidify the greenhouse.

Providing heat to the air, the plant canopy

Forced air systems are standard in Alberta greenhouses. Overhead natural gas burning furnaces are normally located at one end of the greenhouse which move the heated air down the length of the greenhouse to the far end. There are a number of types of forced air systems and all try to ensure that the heat is adequately distributed throughout the greenhouse to maintain the environmental air temperature setpoints. Boilers and pipe and fin systems can also be used to provide heat to the air. The main consideration for heating the air is uniform distribution of the heat throughout the entire greenhouse so that the entire plant canopy is equally affected.

Providing heat to the root zone

The most common system to provide heat to the floor or root zone is the "pipe and rail" system. A 5 centimeter (2 inch) diameter steel pipe is placed on the floor between the rows of the crop so that the pipe runs down and returns along the same row approximately 45 centimeters (18 inches) apart. Boilers deliver hot water through this heating pipe. The delivery and return pipe run parallel to one another, forming a "rail" that can be used by carts to run up and down the rows (Figure 4). The carts are useful when working with the plants during pruning and harvest. In this way the heating pipes serve a multiple use.

Providing heat to the "heads" of the plants

The term "plant head" is not likely to found in any botany textbook, it is a term used by greenhouse vegetable growers to refer to the tops of the plant where the growing points are actively developing new shoot, leaves, flowers and young fruit (Portree 1996). Some growers run hot water fin pipe 15 centimeters (6 inches) above the head in order to obtain a more precise control of temperatures. This optimizes pollination of the flowers as well as early stages of fruit and leaf development. This pipe is raised as the crop grows. Currently this system is not commonly employed by Alberta greenhouse vegetable growers.

Figure 6. Pipe and rail floor heat and electric cart.

Ventilation and Air Circulation

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Ventilation Systems

The ventilation system provides the means by which the greenhouse air is circulated, mixed and exchanged. It allows for a more uniform climate and helps to distribute heat from the heating system (Jackson and Darby 1990) as well as removing heat from the greenhouse when cooling is required. In combination with the heating system, ventilation also provides a means for dehumidifying the greenhouse environment. Ventilation is required throughout the year, however the ventilation required varies with the outside environment. During the winter months ventilation is required primarily for dehumidification, as warm, humid air is exhausted, cool, dry air is brought in. The important consideration when bringing in cold air is proper mixing with the main mass of greenhouse air in order to minimize the negative effects of the cold air contacting the plants. Maximum winter ventilation rates usually do not exceed fifteen air changes per hour (Jackson and Darby 1990).

Figure 7. Ridge vent.

Under Alberta conditions summer ventilation primarily serves to aid in cooling the crop, venting for dehumidification is usually not the goal. In fact, in southern Alberta, maintaining humid air is often the concern. Summer ventilation is triggered primarily by temperature setpoints, and as air is moved through the greenhouse to remove heat, humidity is also lost. So much so, it is difficult to maintain optimum relative humidity levels without also having mist systems or other cooling systems in place. Maximum summer air exchange rates are in the range of 1 complete air exchange per minute.

Ventilation systems can be primarily mechanical; relying on exhaust fans or, natural; relying on the natural upward movement of hot air to exit the greenhouse through ridge or gutter vents. The mechanical or forced air ventilation can be costly, both for the purchase, and for the operation of the equipment (Jackson and Darby 1990). However, forced ventilation is required in order for some evaporative cooling systems to function.

Air Circulation, Horizontal Air Flow (HAF) Fans

Additional air circulation within the greenhouse can provide for more uniform distribution ofcarbon dioxide, humidity and temperature, especially during the winter (Brugger et al. 1987). Used in combination with the ventilation system, recirculating fan systems ensure the cold air brought in by the ventilation system mixes uniformly with the warm inside air (Jackson and Darby 1990). The fans are relatively inexpensive to operate, and are located to move air along the length of the greenhouse, with the direction of movement alternating between adjacent bays (Blom et al 1991). The fans must be adequately sized to ensure that proper mixing of the air occurs (Jackson and Darby 1990), without the fans being over-sized which can cause excessive air movement reducing yield (Brugger et al. 1987). The general recommendation for sizing is a fan capacity of 0.9 to 1.1 cubic meters per minute per square meter of floor area with a velocity no greater that 1 meter per second across the plants (Brugger et al. 1987, Jackson and Darby 1990).

Cooling and Humidification

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

During periods of high light intensity, air temperatures rise inside the greenhouse and cooling is required. Increasing ventilation rates serves to bring cooler, outside air into the greenhouse, but during the typical Alberta summer months, ventilation alone is often not enough to maintain optimum greenhouse air temperatures. Alberta growers depend on cooling systems to ensure optimum growing temperatures are maintained. These cooling systems also serve to humidify the greenhouse. Requirements for cooling and humidification vary depending on location within the

province. Southern Alberta growers generally contend with harsher summer growing conditions, higher outside temperatures and lower outside relative humidity, than growers in central Alberta. In areas of the province where cooling is required, evaporative cooling systems are being used. Evaporative cooling is most effective in areas where the outside relative humidity is less than 60% (Jackson and Darby 1990).

Pad and Fan Evaporative Cooling

Figure 8. Evaporative pad.

As the name implies, evaporative cooling pads are used in conjunction with mechanical ventilation systems to reduce the temperatures within the greenhouse. The principle of the system is the outside air is cooled by drawing it through continually wetted pads. Pad systems work best in tightly built greenhouses because they require the air entering the greenhouse to first pass through the pad rather than holes or gaps in the walls (Jackson and Darby 1990). If the greenhouse is not tight, the incoming air will bypass the evaporative pads as the pads provide more resistance to air movement. Exhaust fans at the opposite end of the greenhouse provide the necessary energy to draw the outside air through the pads. As the air passes through the pad and is cooled, the air also takes up water vapour and adds humidity to the greenhouse.

Mist systems

Both high and low-pressure mist systems are used for cooling and adding humidity to the greenhouse (Jackson and Darby 1990). Mist systems can be employed in both mechanically and naturally ventilated greenhouses. Mist systems work by forcing water through nozzles which break up the water into fine droplets. This process allows the droplets to evaporate fairly quickly into the air. As the evaporation of water requires heat from the environment, the air is cooled. Misting systems must be carefully controlled to provide the required cooling without increasing the relative humidity beyond optimum levels for plant performance, or allowing free water to form on the plants which can encourage the development of disease.

If the quality of the water used for misting is poor, there is the possibility of mineral salts being deposited on the leaves and fruit, which could

result in reduced fruit quality and yield loss. Figure 9. High pressure mist nozzle.

Greenhouse Floors

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Preparation of the greenhouse floor for greenhouse vegetable production is important to the overall operation of the greenhouse. The floor is contoured so that low spots, which would allow for the pooling of water, are eliminated. Small channels are placed in association with the crop rows with one channel running the length of the single or double row. These channels allow for any drainage from irrigation to the plants to be carried to one end of the greenhouse to the holding tanks for recirculation. These channels are approximately 15 centimeters wide by 15 centimeters deep (6 inches by 6 inches). The depth varies slightly from one end of the channel to the other so the water is intended to drain towards a common end of the greenhouse where another channel carries the water towards a reservoir in the floor located in one corner of the greenhouse. The floor is covered with white plastic film to seal-off the soil from the greenhouse environment, reducing the problems associated with soil-borne plant diseases and weed problems. The plants are rooted in bags or slabs of growing media placed on top of the plastic floor. The white plastic also serves to reflect any light reaching the floor back up into the plant canopy. Estimations place the amount of light reflected back into the crop by white plastic floors to be about 13% of the light reaching the floor, and can increase crop yield (Wilson et al 1992). Due to the large area under production, concrete floors are generally too expensive. A concrete walk-way is a practical necessity, usually running the width of the greenhouse along one end wall. This walkway allows for the efficient, high traffic movement of staff within the greenhouse and produce out of the greenhouse.

Carbon Dioxide Supplementation

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Carbon dioxide (CO2) plays an important role in increasing crop productivity (Rijkdijk and Houter 1993). An actively photosynthesizing crop will quickly deplete the CO2 from the greenhouse environment (Rijkdijk and Houter 1993). In summer, even with maximum ventilation, CO2 levels within the typical Alberta vegetable production greenhouse typically fall below ambient levels of CO2 [below 350 parts per million (350 ppm)]. It has been estimated that if the amount of CO2 in the atmosphere doubled to 700 ppm, the yield of field crops should

increase by 33% (Tremblay and Gosselin 1998). Optimum CO2 targets in the greenhouse atmosphere are generally accepted to be approximately 700 to 800 ppm (Portree 1996).

Carbon Dioxide Supplementation via Combustion

As carbon dioxide is one of the products of combustion, this process can be used to introduce CO2 into the greenhouse. The major concern with using combustion is CO2 is only one of the products of combustion. Other gases which can be produced by the combustion process, are detrimental to crop production (see section 5.5, Air pollution in the greenhouse). The production of pollutant gases from combustion is dependent on the type and quality of the fuel used for combustion and whether complete combustion occurs (faulty burners) (Blom 1998). Natural Gas CO2 Generators One method of CO2 supplementation in Alberta greenhouses is the use natural gas burning CO2 generators placed throughout the greenhouse above the crop canopy. Under lower light, low ventilation conditions, these generators can effectively maintain optimum CO2 levels. However, the experience with these generators during periods of intense summer sunlight, it is that it is still difficult to maintain ambient CO2 levels in the crop. Also, since the combustion process takes place in the greenhouse, the heat of combustion contributes to driving the greenhouse temperatures higher, increasing the need for cooling. Even distribution of the CO2 throughout the crop is also difficult to obtain as the CO2 originates from point sources above the canopy. A fresh air intake should be provided when using these

Figure 10. Natural gas CO2 generators. Boiler Stack Recovery Systems Stack recovery systems are receiving more attention by Alberta growers. This system requires a clean burning high output boiler and a system to recover the CO2 from the exhaust stack for distribution to the crop. The CO2 is directed through pipes placed within the rows of the crop, this way the CO2 distribution is improved by introducing the CO2 right to the plant canopy.

Carbon monoxide can also be present in the exhaust gas and sensors are used to regulate the delivery of exhaust gas into the greenhouse and ensure that carbon monoxide levels do not rise to unsafe levels.

Liquid CO2 Supplementation

Liquid CO2 is another alternative for supplementation. The advantage with liquid CO2 is that it is a clean source of CO2 for the greenhouse, as the other byproducts of combustion are not present. For this reason liquid CO2 is especially advantageous for use on sensitive seedling plants early in the crop season (Portree 1996). Distribution to the crop can be accomplished through a system of delivery pipes to the crop canopy as with the stack recovery systems. The draw-back to the use of liquid CO2 has been the cost. It has historically been less expensive to obtain CO2 through the combustion of natural gas than by buying liquid carbon dioxide. Recent work at CDC South in Brooks has developed a cost effective method for liquid CO2 supplementation under Alberta greenhouse growing conditions.

Figure 11. Liquid CO2 tank.

Irrigation and Fertilizer Feed Systems

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

The fertilizer and irrigation systems provide control on the delivery of water and nutrients to the plants. The two systems complement each other to deliver precise amounts of water and fertilizer to the plants as frequently as required. There are a number of variations on the theme, however the basic requirements are incoming water is injected or amended with precise amounts of fertilizer before it is delivered to the plants. One key point to keep in mind is that every time a plant is watered, it also receives fertilizer. Pumps deliver the fertilizer and water through hoses running the length of each of row. Small diameter tubing, spaghetti tubes, come off the hose with

one tube generally feeding one plant. The systems are designed so the amount of fertilizer and water delivered to the plants is equal throughout the greenhouse. Larger greenhouses are often partitioned into a number of zones for watering, with each zone watered sequentially in-turn once a watering event is required, and with the watering modified independently in each zone as required. Recirculating systems add another level of complexity to the process. In most modern vegetable greenhouses, a certain percentage of the water delivered to the plants on a daily basis is allowed to flow past the root system. The water that flows past the plant roots is referred to as the "leachate". The principles of leaching as well as how to fertilize and water the crop, is explained in more detail in section 5.7.5 Application of fertilizer and water. Recirculating systems are designed to collect the leachate for reuse in the crop. Reusing the leachate minimizes the loss of fertilizer and water from the greenhouse to the environment. Before the leachate can be reused, it must first be treated to kill any disease organisms which may have accumulated in the system. A number of methods for treatment are available and include UV light (Weiler and Sailus 1996), ozone treatment (Weiler and Sailus 1996), heat pasteurization (Portree 1996, Weiler and Sailus 1996) and biofiltration (Ng and van der Gulik 1999).

Computerized Environmental Control Systems

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Computerized environmental control systems allow growers the ability to integrate the control of all the systems involved in manipulating the greenhouse environment. The effect is to turn the entire greenhouse and its component systems into a single instrument for control, where optimum environmental parameters are defined, and control is the result of the on-going input of the component systems acting in concert.

Figure 12. Computerized environmental control system.

Virtually all computer programs for controlling the greenhouse environment provide for optimal plant growth (Lange and Tantau 1996). There are a wide variety of computerized control systems which are on the market. Generally, the higher the degree of integration of control of the various component systems ie. heating, cooling, ventilation and irrigation systems, the higher the cost of the computer system.

Optimization of the

environment for maximum crop production requires timely responses to changes in the environment and the changing requirements of the crop.

The greenhouse environment changes as the crop responds to its environment, and the environment changes in response to the activity of the crop. Fast crop processes, such as photosynthesis are considered to respond instantaneously to the changing environment (Seginer 1996). Due to the dynamics of the greenhouse, the inertia of the environment, it takes longer to implement changes to the environment, upwards of 15 minutes (Seginer 1996). Much of the disturbance to the greenhouse environment is due to the outside environment, the normal cycle of the day - night periods, outside temperatures, the effects of scattered clouds on an otherwise sunny day (Seginer 1996). The environmental control system has to continually work to modify the environment to optimize crop performance in response to on-going change of the dynamic environment. The ability of a computer system to control the environment is only as good as the information it receives from the environment. The computer's contact with the environment occurs through various sensors recording temperature, relative humidity, light levels and CO2 levels. It is important that quality sensors are used and routinely maintained to ensure that they are operating properly. Sensor placement is also important to ensure accurate readings of the crop environment, for example, a temperature sensor placed in direct sunlight is going to give a different set of readings than a temperature sensor placed within the crop canopy.

Figure 13. Environmental sensor box.

Management of the Greenhouse Environment

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

This section looks at how the tools that growers have at their disposal to control the environment, are manipulated with respect to the important environmental influences on plant growth and development, for the actual optimization of the greenhouse environment. As stated in "Concepts Involved in the Optimization of the Greenhouse Environment for Crop Production," the primary goal of optimization of the greenhouse environment is to maximize the photosynthetic process in the crop. The strategy used to maximize photosynthesis is through the management of transpiration. Therefore, on-going modifications are made to the greenhouse environment to manage the transpiration of the crop to match the maximum rate of photosynthesis. Growth can be defined as an increase in biomass (Papadopoulos and Pararajasingham 1997). The increase in size of a plant or other organism can also be considered as the fundamental definition of growth (Salisbury and Ross 1978). The growth of plants is associated with changes in the numbers of plant organs occurring through the initiation of new leaves, stems and fruit, abortion of leaves and fruit, and physiological development of numbers from one age class to the next (Jones et al 1989). Managing growth and development of an entire crop for maximum production involves the manipulation of temperature and humidity to obtain not only the maximum rate of photosynthesis under the given light conditions, but also the optimum balance of vegetative and generative growth of plants for sustained production and high yields (Portree 1996). This implies that growers can direct the results of photosynthesis, the production of assimilates, sugars and starches, towards both vegetative and generative in a balance. Generative growth is the growth associated with fruit production. For maximum fruit production to occur, the plant has to be provided both with the appropriate cues to trigger the setting of fruit and the cues to maintain adequate levels of stem and leaf development. The balance is achieved when the assimilates from photosynthesis are directed towards maintaining the production of the new leaves and stems required to support the continued production of fruit. The appropriate cues are provided through the manipulation of the environment, and are subject to change depending on the behavior of the crop. Careful attention must be paid to the signals given by the plant, the indicators of which direction the plant is primarily headed, vegetative or generative, and how corrective action is applied through further manipulation of the environment to maintain high production.

Light

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Light limits the photosynthetic productivity of all crops (Wilson et al 1992) and is the most important variable affecting productivity in the greenhouse (Wilson et al 1992, Papadopoulos and Pararajasingham 1997). The transpiration rate of any greenhouse crop is the function of three variables; ambient temperature, humidity and light (Stanghellini and Van Meurs 1992, Van Meurs and Stanghellini 1992). Of these three, it is light which is usually out of our control as it is received from the sun (Stanghellini and Van Meurs 1992, Van Meurs and Stanghellini 1992). Supplementary lighting does offer opportunity to increase yield during low light periods, but is generally considered commercially unprofitable (Warren et al 1992, Papadopoulos and Pararajasingham 1997). The other means for manipulating light are limited to screening or shading (Stanghellini and Van Meurs 1992) and are employed when light intensities are too high. However, there are also general strategies to help maximize the crop's access to the available light in the greenhouse.

Properties of Light and its Measurement

In order to understand how to control the environment to make the maximum use of the available light in the greenhouse, it is important to know about the properties of light and how light is measured. Considerable confusion has existed regarding the measurement of light (LI-COR Inc.), however it is worthwhile for growers to approach the subject. Light has both wave properties and properties of particles or photons (Tilley 1979). Depending on how light is considered, the measurement of light can reflect either its wave or particle properties. Different companies provide a number of different types of light sensors for use with computerized environmental control systems. As long as the sensors measure the light available to plants, for practical purposes it is not as important how light is measured, as it is for growers to be able to relate these measurements to how the crop is performing.

Light is a form of radiation produced by the sun, electromagnetic

Figure 14. The visible spectrum.

radiation. A narrow range of this electromagnetic radiation falls within the range of 400 to 700 nanometers (nm) of wavelength. One nanometer being equal to 0.000000001 meters. The portion of the electromagnetic spectrum which falls between 400 to 700 nm is referred to as the spectrum of visible light, this is essentially the range of the electromagnetic spectrum that can

be seen. Plants respond to light in the visible spectrum and use this light to drive photosynthesis.

Figure 15. The photosynthetic action spectrum.

Photosynthetically Active Radiation (PAR) is defined as radiation in the 400 to 700 nm waveband. PAR is the general term which covers both photon terms and energy terms ( LI-COR Inc.). The rate of flow of radiant (light) energy in the form of an electromagnetic wave is called the radiant flux, and the unit used to measure this is the Watt (W). The units of Watts per square meter (W/m²) are used by some light meters and is an example of an "instantaneous" measurement of PAR (LI-COR Inc.). Other meters commonly seen in greenhouses take "integrated" measurements reporting in units of joules per square centimeter (j/cm²) (LI-COR Inc.). Although the units seem fairly similar, there is no direct conversion between the two. Photosynthetic Photon Flux Density (PPFD) is another term associated with PAR, but refers to the measurement of

light in terms of photons or particles. It is also sometimes referred to as Quantum Flux Density (LI-COR Inc.). Photosynthetic Photon Flux Density is defined as the number of photons in the 400 - 700 nm waveband reaching a unit surface per unit of time (LI-COR Inc.). The units of PPFD are micromoles per second per square meter (micromol/m²). As the scientific community begins to agree on how best to measure light there may be more standardization in light sensors and the units used to describe the light radiation reaching a unit area. Greenhouse growers will still be left with the task of making day-to-day meaning of the light readings with respect to control of the overall environment. Generally speaking, the more intense the light, the higher the rate of photosynthesis and transpiration (increased humidity), as well as solar heat gain in the greenhouse. Of these, it is heat gain which usually calls for modification of the environment as temperatures rise on the high end of the optimum range for photosynthesis, and ventilation and cooling begins. Plants also require more water under increasing light levels.

The Light Use Efficiency of Plants

Plants use the light in the 400 to 700 nm range for photosynthesis, but they make better use of some wavelengths than others. Figure 15 presents the photosynthetic action spectrum of plants, the relative rate of photosynthesis of plants over the range of PAR, photosynthetically available light. All plants show a peak of light use in the red region, approximately 650 nm and a smaller peak in the blue region at approximately 450 nm (Salisbury and Ross 1978). Plants are relatively inefficient at using light and are only able to use about a maximum of 22% of the light absorbed

in the 400 to 700 nm region (Salisbury and Ross 1978). Light use efficiency by plants depends not only on the photosynthetic efficiency of plants, but also on the efficiency of the interception of light (Wilson et al 1992).

Maximizing the Crop's Access to Available Light

The high cost of greenhouse production requires growers to maximize the use of light falling on the greenhouse area ( Wilson et al 1992). Before the crops are able to use the light, it first has to pass through the greenhouse covering, which does not transmit light perfectly. The greenhouse intercepts a percentage of light falling on it allowing a maximum of 80% of the light to reach the crop at around noon, with an overall average of 68% over the day (Wilson et al 1992). However, the greenhouse covering also partially diffuses or scatters the light coming into the greenhouse so that it is not all moving in one direction (Wilson et al 1992). The implication of this is scattered light tends to reach more leaves in the canopy than directional light which throws more shadows. It is important that the crop be orientated in such a way that the light transmitted through the structure is optimized to allow for efficient distribution to the canopy. Greenhouse vegetable crops have a vertical structure in the greenhouse, so light filters down through "layers" of leaves before a smaller percentage actually reaches the floor. Leaf area index (LAI) is widely used to indicate the ratio of the area of leaves over the area of ground which the leaves cover (Salisbury and Ross 1978). Leaf area indexes of up to 8 are common for many mature crop communities, depending on species and planting density (Salisbury and Ross 1978). Mature canopies of greenhouse sweet peppers have a relatively high leaf area index of approximately 6.3 when compared to greenhouse cucumbers and tomatoes at 3.4 to 2.3 respectively (Hand et al 1993). The optimum leaf area index varies with the amount of sunlight reaching the crop. Under full sun, the optimum LAI is 7, at 60% of full sun the optimum is 5, at 23% full sunlight, the optimum is only 1.5 (Salisbury and Ross 1978). This point has application to a growing and developing crop. In Alberta, vegetable crops are seeded in November to December, the low light period of the year. Young crops have lower leaf area indexes which increase as the crop ages. Under this crop cycle, the plants are growing and increasing their LAI as the light conditions improve. Crop productivity increases with LAI up to a certain point because of more efficient light interception, as LAI increases beyond this point no further efficiency increases are realized, and in some cases decreases occur (Salisbury and Ross 1978). There is also a suggestion that an efficient crop canopy must allow some penetration of PAR below the uppermost leaves, and the sharing of light by many leaves is a prerequisite of high productivity (Papadopoulos and Pararajasingham 1997). Leaves can be divided into two groups; sun leaves that intercept direct radiation and shade leaves, that receive scattered radiation (Wilson and Loomis 1967, Papadopoulos and Pararajasingham 1997). The structures of these leaves are distinctly different (Wilson and Loomis 1967).

The major greenhouse vegetable crops (tomatoes, cucumbers and peppers) are arranged in either single or double rows (Wilson et al 1992, Hand et al 1993). This arrangement of the plants and subsequent canopy represents an effective compromise between accessibility to work the crop, and light interception by the crop (Hand et al 1993). For a greenhouse pepper crop, this canopy provides for light interception exceeding 90% under overcast skies and 94% for much of the day under clear skies (Hand et al 1993). There is a dramatic decrease in interception that occurs around noon, and lasts for about an hour when the sun aligns along the axis of north - south aligned crop rows. Interception falls to 50% at the gap centers where the remaining light reaches the ground, and the overall interception of the canopy drops to 80% (Hand et al 1993). The strategies to reduce this light loss would be to align the rows east-west instead of north-south, reduced light interception occurring when the sun aligns with the rows would take place early and late in the day when the light intensities are already quite low (Hand et al 1993). The use of white plastic ground cover can reflect back light that has penetrated the canopy and can result in an overall increase of 9% over crops without white plastic ground cover (Wilson et al 1992, Hand et al 1993). The effect of row orientation varies with time of the day, season, latitude and canopy geometry (Papadopoulos and Pararajasingham 1997). It has been demonstrated that at 34° latitude, north-south orientated rows of tall crops, such as tomatoes, cucumbers and peppers, intercepted more radiation over the growing season than those orientated east-west (Papadopoulos and Pararajasingham 1997). This finding was the opposite for crops grown at 51.3° latitude (Papadopoulos and Pararajasingham 1997). The majority of greenhouse vegetable crop production in Alberta occurs between 50° (Redcliff) and 53° (Edmonton) North. This would suggest that the optimum row alignment of tall crops for maximum light interception over the entire season, would be east-west. However, in Alberta, high yielding greenhouse vegetable crops are grown in greenhouses with north-south aligned rows as well as in greenhouses with east-west aligned rows. Alberta is known for its sunshine, and the sun is not usually limiting during the summer. In fact, many vegetable growers apply whitewash shading to the greenhouses during the high light period of the year because the light intensity and associated solar heat gain can be too high for optimal crop performance. The strategies for increasing light interception by the canopy should focus specifically on the times in year when light is limiting, for Alberta, this is early spring and late fall. When light is limiting, a linear function exists between light reduction and decreased growth, with a 1% increase in growth occurring with a 1% increase in light (De Koning 1989, Wilson et al 1992) under light levels up to 200 W/m². When light levels are limiting, supplementary artificial lighting will increase plant growth and yield (Papadopoulos and Pararajasingham 1997). The use of supplemental lighting has its limits as well. Using supplemental lighting to increase the photoperiod to 16 and 20 hours increased the yield of pepper

plants while continuous light decreased yields compared to the 20 hour photoperiod (Demers and Gosselin 1998). The economics of artificial light supplementation generally do not warrant the use of supplementary light on a greenhouse vegetable crop in full production. However, supplementary lighting of seedling vegetable plants prior to transplanting into the production greenhouse is recommended for those growers growing their own plants from seed. Light is generally limiting in Alberta when greenhouse vegetable seedlings are started in November to December. Using supplemental lighting for seedling transplant production when natural light is limiting resulted in increased weight of tomato and pepper transplants grown under supplemental light compared to control transplants grown under natural light (Demers et al 1991, Fierro et al 1994). Young plants exposed to supplemental light also were ready for transplanting 1 to 2 weeks earlier than plants grown under natural light (Demers et al 1991). When supplemental lighting was combined with carbon dioxide supplementation at 900 ppm, not only did the weight of the transplants increase, but total yield of the tomato crop was also higher by 10% over the control plants (Fierro et al 1994). It is recommended that supplementary lighting be used for production of vegetable transplant production in Alberta during the low light period of the year. This translates to about 4 to 7 weeks of lighting depending on the crop. Greenhouse sweet peppers are transplanted into the production greenhouse at 6 to 7 weeks of age. The amount of light required varies with crop but ranges between approximately 120 - 180 W/m², coming from 400 W lights. A typical arrangement of lights for the seedling/transplant nursery would be to have the lights in rows 1.8 m (6 ft) off the floor, spaced at 2.7 m (9 ft.) along the rows with 3.6 m (12 ft) between the rows of lights .

Figure 16. High pressure sodium light.

Natural light levels vary throughout the province with areas in southern Alberta at 50° latitude receiving 13% more light annually than areas around Edmonton at 53° latitude (Mirza 1990). Strategies to optimize the use of available light for commercial greenhouse production involve a number of crop management variables. Row orientation, plant density, plant training and pruning, maintaining optimum growing temperatures and relative humidity levels, CO2 supplementation, and even light supplementation, all play a role. All the variables must be optimized for a given light level for a given crop, and none of these variables are independent from one another. How a grower manipulates one variable, affects the others.

Temperature Management

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Development and flowering of plants relates to both root zone and air temperature (Khah and Passam 1992), and control of temperature is an important tool for the control of crop growth (De Koning 1996).

Managing Air Temperatures

The optimum temperature is determined by the processes involved in the utilization of assimilate products of photosynthesis, ie. distribution of dry matter to shoots, leaves, roots and fruit (De Koning 1996). For the control of crop growth, average temperature over one or several days is more important than the day/night temperature differences (Bakker 1989, De Koning 1996). This average temperature is also referred to as the 24-hour average temperature or 24-hour mean temperature (Bakker 1989, Portree 1996). Various greenhouse crops show a very close relationship between growth, yield and the 24-hour mean temperature (Bakker 1989, Portree 1996). With the goal of directing growth and maintaining optimum plant balance for sustained high yield production, the 24-hour mean temperature can be manipulated to direct the plant to be more generative in growth, or more vegetative in growth. Optimum photosynthesis occurs between 21 to 22 °C (Portree 1996), this temperature serves as the target for managing temperatures during the day when photosynthesis occurs. Optimum temperatures for vegetative growth for greenhouse peppers is between 21 to 23 °C, with the optimum temperature for yield about 21 °C (Bakker 1989). Fruit set, however, is determined by the 24-hour mean temperature and the difference in day - night temperatures (Bakker 1989), with the optimum night temperature for flowering and fruit setting at 16 to 18 °C (Pressman 1998). Target 24-hour mean temperatures for the main greenhouse vegetable crops (cucumbers, tomatoes, peppers) can vary from crop to crop with differences even between cultivars of the same crop. The 24-hour mean temperature optimums for vegetable crops range between 21 to 23 °C, depending on light intensity. The general management strategy for directing the growth of the crop is to raise the 24-hour average temperature to push the plants in a generative direction and to lower the 24-hour average temperature to encourage vegetative growth (Portree 1996). Adjustments to the 24-hour mean temperature are made usually within 1 to 1.5& deg;C with careful attention paid to the crop response. One assumption that is made when using air temperature as the guide to directing plant growth is that it represents the actual plant temperature. The role of temperature in the optimization of plant performance and yield is ultimately based on the temperature of the plants. Plant temperatures are usually within a degree of air temperature, however during the high light periods of the year, plant tissues exposed to high light can reach 10 to 12 °C higher than air temperatures. It is important to be aware of this fact and to

use strategies such as shading and evaporative cooling to reduce overheating of the plant tissues. Infrared thermometers are useful for determining actual leaf temperature. Precision Heat in the Canopy Precision heating of specific areas within the crop canopy add another dimension of air temperature control beyond maintaining optimum temperatures of the entire greenhouse air mass. Using heating pipes that can be raised and lowered, heat can be applied close to flowers and developing fruit to provide optimum temperatures for maximum development in spite of the day - night temperature fluctuations required to signal the plant to produce more flowers. The rate of fruit development can be enhanced with little effect on overall plant development and flower set (De Koning 1996). Precise application of heat in this manner can avoid the problem of low temperatures to the flowers and fruit which are known to disturb flowering and fruit set (Bakker 1989). The functioning of pepper flowers are affected below 14 °C , the number of pollen grains per flower are reduced and fruit set under low night temperatures are generally deformed (Pressman 1998). Problems with low night temperatures can be sporadic in the greenhouse during the cold winter months and can occur even if the environmental control system is apparently meeting and maintaining the set optimum temperature targets. There can be a number of reasons for this, but the primary reasons are 1) lags in response time between the system's detection of the heating setpoint temperature and when the operation of the system is able to provide the required heat throughout the greenhouse and 2) specific temperature variations in the greenhouse due to drafts and "cold pockets".

Managing Root Zone Temperatures

Root zone temperatures are primarily managed to remain in a narrow range to ensure proper root functioning. Target temperatures for the root zone are 18 to 21 °C. Control of the root zone temperature is primarily a concern for Alberta growers in winter, and is obtained through the use of bottom heat systems such as pipe and rail systems. Control is maintained by monitoring the temperature at the roots and maintaining the pipe at a temperature that ensures optimum root zone temperatures. The use of tempered irrigation water is also a strategy employed by some growers. Maintaining warm irrigation water (20 °C is optimum) minimizes the shock to the root system associated with the delivery of cold irrigation water. In cases during the winter months, in the absence of a pipe and rail system, root zone temperatures can drop to 15 °C or lower. The performance of most greenhouse vegetable crops is sub optimal at this low root zone temperature. Using tempered irrigation water alone is not usually successful in raising and maintaining root zone temperatures to optimum levels. The reasons for this are two fold; firstly, the volume of water required for irrigation over the course of the day during the winter months is too small to allow for the adequate sustained warming of the root zone, and secondly, the temperature of the irrigation water would have to be almost hot in order to effect any

immediate change in root zone temperature. Root injury can begin to occur at temperatures in excess of 23 °C in direct contact with the roots. The recommendation for irrigation water temperature is not to exceed 24 - 25 °C. The purpose of the irrigation system is to optimize the delivery of water and nutrients to the root systems of the plants, using it for any other purpose generally compromises the main function of the irrigation system. Systems for controlling root zone temperatures are primarily confined to providing heat during the winter months. During the hot summer months temperatures in the root zone can climb to over 25 °C if the plants are grown in sawdust bags or rockwool slabs, and if the bags are exposed to prolonged direct sunlight. Avoiding high root zone temperatures is accomplished primarily by ensuring an adequate crop canopy to shade the root system. Also, since larger volumes of water are applied to the plants during the summer, ensuring that the irrigation water is relatively cool, approximately 18 °C, (if possible) will help in preventing excessive root zone temperatures. One important point to keep in mind with respect to irrigation water temperatures during the summer months is irrigation pipe exposed to the direct sun can cause the standing water in the pipe to reach very high temperatures, in excess of 35 °C! Irrigation pipe is often black to prevent light penetration into the line which can result in the development of algae and the associated problems with clogged drippers. It is important to monitor irrigation water temperatures at the plant dripline, especially during the first part of the irrigation cycle, to ensure that the temperatures are not too high. All exposed irrigation pipe should be shaded with white plastic or moved out of the direct sunlight if a problem is detected.

Management of Relative Humidity Using Vapour Pressure Deficits

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Plants exchange energy with the environment primarily through the evaporation of water, through the process of transpiration (Papadakis et al 1994). Transpiration is the only type of transfer process in the greenhouse that has both a physical and biological basis (Papadakis et al 1994). This plant process is almost exclusively responsible for the subtropical climate in the greenhouse (Papadakis et al 1994). Seventy percent of the light energy falling on a greenhouse crop goes towards transpiration, the changing of liquid water to water vapour (Hanan 1990), and most of the irrigation water applied to the crop is lost through transpiration (Papadakis et al 1994). Relative humidity (RH) is a measure of the water vapour content of the air. The use of relative humidity to measure the amount of water in the air is based on the fact that the ability of the air to hold water vapour is dependent on the temperature of the air. Relative humidity is defined as the amount of water vapour in the air compared to the maximum amount of water vapour

the air is able to hold at that temperature (Tilley 1979, Portree 1996). The implication of this is that a given reading of relative humidity reflects different amounts of water vapour in the air at different temperatures. For example air at a temperature of 24 °C at a RH of 80% is actually holding more water vapour than air at a temperature of 20 °C at a RH of 80%. The use of relative humidity for control of the water content of the greenhouse air mass has commonly been approached by maintaining the relative humidity below threshold values, one for the day and one for the night (Stanghellini and Van Meurs 1992). This type of humidity control was directed at preserving low humidity (Stanghellini and Van Meurs 1992), and although humidity levels high enough to favour disease organisms must be avoided (Stanghellini and Van Meurs 1992), there are more optimal approaches to control the humidity levels in the greenhouse environment. The sole use of relative humidity as the basis of controlling greenhouse air water content does not allow for optimization of the growing environment, as it does not provide a firm basis for dealing with plant processes such as transpiration in a direct manner. (Hanan 1990). The common purpose of humidity control is to sustain a minimal rate of transpiration (Stanghellini and Van Meurs 1992). The transpiration rate of a given greenhouse crop is a function of three in-house variables: temperature, humidity and light (Stanghellini and Van Meurs 1992, Van Meurs and Stanghellini 1992). Light is the one variable usually outside the control of most greenhouse growers. If the existing natural light levels are accepted, then crop transpiration is primarily determined by the temperature and humidity in the greenhouse (Stanghellini and Van Meurs 1992). Achievement of the optimum "transpiration setpoint" depends on the management of temperature and humidity within the greenhouse. More specifically, at each level of natural light received into the greenhouse, a transpiration setpoint should allow for the determination of optimal temperature and humidity setpoints (Stanghellini and Van Meurs 1992). The relationship between transpiration and humidity is awkward to describe, as it is largely related to the reaction of the stomata to the difference in vapour pressure between the leaves and the air (Stanghellini and Van Meurs 1992). The most certain piece of knowledge about how stomata behave under increasing vapour pressure difference is it is dependent on the plant species in question (Stanghellini and Van Meurs 1992). However, even with the current uncertainties with understanding the relationships and determining mechanisms involved, the main point to remember about environmental control of transpiration is that it is possible (Stanghellini and Van Meurs 1992, Van Meurs and Stanghellini 1992). The concept of vapour pressure difference or vapour pressure deficit (VPD) can be used to establish setpoints for temperature and relative humidity in combination to optimize transpiration under any given light level. VPD is one of the important environmental factors influencing the growth and development of greenhouse crops (Zabri and Burrage 1997), and offers a more accurate characteristic for describing water saturation of the air than

relative humidity because VPD is not temperature dependent (Rodov et al 1995). Vapour pressure can be thought of as the concentration, or level of saturation of water existing as a gas, in the air (Tilley 1979). As warm air can hold more water vapour than cool air, so the vapour pressures of water in warm air can reach higher values than in cool air. There is a natural movement from areas of high concentration to areas of low concentration. Just as heat naturally flows from warm areas to cool areas, so does water vapour move from areas of high vapour pressure, or high concentration, to areas of low vapour pressure, or low concentration. This is true for any given air temperature. The vapour pressure deficit is used to describe the difference in water vapour concentration between two areas. The size of the difference also indicates the natural "draw" or force driving the water vapour to move from the area of high concentration to low concentration. The rate of transpiration, or water vapour loss from a leaf into the air around the leaf, can be thought of, and managed using the concept of vapour pressure deficit (VPD). Plants maintained under low VPD had lower transpiration rates while plants under high VPD can experience higher transpiration rates and greater water stress (Zabri and Burrage 1997). A key point when considering the concept of VPD as it applies to controlling plant transpiration is the vapour pressure of water vapour is always higher inside the leaf than outside the leaf. Meaning the concentration of water vapour is always greater within the leaf than in the greenhouse environment, with the possible exception of having a very undesirable 100% relative humidity in the greenhouse environment. This means the natural tendency of movement of water vapour is from within the leaf into the greenhouse environment. The rate of movement of water from within the leaf into the greenhouse air, or transpiration, is governed largely by the difference in the vapour pressure of water in the greenhouse air and the vapour pressure within the leaf. The relative humidity of the air within the leaf can be considered to always be 100% (Papadakis et al 1994), so by optimizing temperature and relative humidity of the greenhouse air, growers can establish and maintain a certain rate of water loss from the leaf, a certain transpiration rate. The ultimate goal is to establish and maintain the optimum transpiration rate for maximum yield. Crop yield is linked to the relative increase or decrease in transpiration, a simplified relationship relates increase in yield to increase in VPD (Jolliet et al 1993) Transpiration is a key plant process for cooling the plant, bringing nutrients in from the root system and for the allocation of resources within the plant. Transpiration rate can determine the maximum efficiency by which photosynthesis occurs, how efficiently nutrients are brought into the plant and combined with the products of photosynthesis, and how these resources for growth are distributed throughout the plant. Since the principles of VPD can be used to control the transpiration rate, there is a range of optimum VPDs corresponding to optimum transpiration rates for maximum sustained yield (Portree 1996).

The measurement of VPD is done in terms of pressure, using units such as millibars (mb) or kilopascals (kPa) or units of concentration, grams per cubic meter (g/m3). The units of measurement can vary from sensor to sensor, or between the various systems used to control VPD. The optimum range of VPD is between 3 to 7 grams/m3 (Portree 1996), and regardless of how VPD is measured, maintaining VPD in the optimum range can be obtained by meeting specific corresponding relative humidity and temperature targets. Table 1 presents the temperature - relative humidity combinations required to maintain the range of optimal VPD inthe greenhouse environment. It is important to remember that this table only displays the temperature and humidity targets to obtain the range of optimum VPDs, it does not consider the temperature targets that are optimal for specific crops. There is a range of optimal growing temperatures for each crop that will determine a narrower band of temperature - humidity targets for optimizing VPD. Table 1. Relative Humidity and Temperature Targets to Obtain Optimal Vapour Pressure Deficitss Gram/m3* and millibars (mb)

Relative Humidity

Temp

oC

95% 90 % 85 % 80 % 75 % 70 % 65 % 60 % 55 % 50 %

gm/m3

mb

gm/m3

mb

gm/m3

mb

gm/m3

mb

gm/m3

mb

gm/m3

mb

gm/m3

mb

gm/m3

mb

gm/m3

mb

gm/m3

mb

15 0.5

0.6 1.1

1.4 1.7

2.2 2.2

2.9 2.8

3.7 3.3

4.3 3.9

5.1 4.4

5.8 5.0

6.6 5.5

7.2

16 0.6

0.8 1.2

1.6 1.8

2.4 2.3

3.0 2.9

3.8 3.5

4.6 4.1

5.4 4.7

6.2 5.3

7.0 5.8

7.6

17 0.6

0.8 1.3

1.7 1.9

2.5 2.5

3.3 3.1

4.1 3.7

4.9 4.3

5.6 5.0

6.6 5.6

7.4 6.2

8.1

18 .07

0.9 1.3

1.7 2.0

2.6 2.7

3.6 3.3

4.3 4.0

5.3 4.6

6.1 5.3

7.0 5.9

7.8 6.6

8.7

19 .07

0.9 1.4

1.8 2.1

2.8 2.9

3.8 3.6

4.7 4.3

5.6 5.0

6.6 5.7

7.5 6.4

8.4 7.1

9.3

20 .08

1.0 1.5

2.0 2.2

2.9 3.0

3.9 3.8

5.0 4.5

5.9 5.3

7.0 6.1

8.0 6.8

8.9 7.5

9.9

21 .08

1.0 1.6

2.1 2.4

3.2 3.3

4.3 4.1

5.4 4.9

6.4 5.7

7.5 6.5

8.6 7.3

9.6 8.1

10.7

22 .09

1.2 1.7

2.2 2.6

3.4 3.5

4.6 4.3

5.7 5.2

6.8 6.0

7.9 6.8

8.9 7.7

10.1

8.6

14.8

23 .09

1.2 1.8

2.4 2.7

3.6 3.7

4.9 4.6

6.1 5.5

7.2 6.4

8.4 7.4

9.7 8.3

10.9

9.2

12.1

24 1.0

1.3 2.0

2.6 3.0

3.9 3.9

5.1 4.9

6.4 5.8

7.6 6.8

8.9 7.8

10.3

8.8

11.6

9.7

12.7

25 1.0

1.3 2.0

2.6 3.0

3.9 4.1

5.4 5.2

6.8 6.2

8.1 7.2

9.5 8.2

10.7

9.2

12.1

10.3

13.6

26 1.1

1.4 2.2

2.9 3.3

4.3 4.4

5.8 5.5

7.2 6.6

8.7 7.7

10.1

8.8

11.6

9.9

13.0

11.0

14.5

27 1.2

1.6 2.4

3.2 3.6

4.7 4.7

6.2 5.9

7.8 7.1

9.3 8.3

10.9

9.4

12.3

10.6

13.9

11.7

15.4

28 1.3

1.7 2.5

3.3 3.7

4.9 5.0

6.6 6.3

8.3 7.5

9.9 8.7

11.4

9.9

13.0

11.2

14.7

12.4

16.3

29 1.4

1.8 2.7

3.6 4.1

5.4 5.3

7.0 6.7

8.8 8.0

10.1

9.3

12.2

10.8

14.2

11.9

15.6

13.2

17.4

30 1.4

1.8 2.8

3.7 4.2

5.5 5.7

7.5 7.1

9.3 8.5

11.2

9.9

13.0

11.3

14.8

12.7

16.7

14.0

18.4

*Optimum range 3-7 grams/m3, 3.9-9.2 mb The plants themselves exert tremendous influence on the greenhouse climate (Lange and Tantau 1996), transpiration not only serves to add moisture to the environment, but is also the mechanism by which plants cool themselves and add heat to the environment (Papadakis et al 1994). Optimization of transpiration rates through management of air temperature and relative humidity can change over the course of the season. Early in the season, when plants are young and the outside temperatures are cold, both heat and humidity (from mist systems) can be applied to maintain temperature and humidity targets. As the season progresses and the crop matures, increasing light intensity increases the transpiration rate and the moisture content of the air. To maintain optimum rates of transpiration, venting is employed to reduce the relative humidity in the air. However, under typical summer conditions in Alberta, particularly in the south, ventilation is almost exclusively triggered by high temperature setpoints calling for cooling. Under these conditions, ventilation can occur continuously throughout the daylight period and results in very low relative humidity in the

greenhouse. As the hot, moist air is vented, it is replaced by still warm, dry air. Southern Alberta is a dry environment with the relative humidity of the air in summer routinely falling below 30%. Under these conditions some form of additional cooling, mist systems or pad and fan evaporative cooling, is required to both reduce the amount of ventilation for cooling as well as to add moisture to the air.

Carbon Dioxide Supplementation

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Carbon dioxide (CO2) is one of the inputs of photosynthesis and as such CO2 plays an important role in increasing crop productivity (Hand 1993, Rijkdjik and Houter 1993). Optimal CO2 concentrations for the greenhouse atmosphere fall with the range of between 700 to 900 ppm (parts per million) (Romero-Aranda et al 1995, Tremblay and Gosselin 1998). Crop productivity depends not only on efficiency of interception of light but also on the efficiency with which light is converted to chemical energy in photosynthesis. Carbon dioxide enrichment to 1200 ppm increases the maximum conversion efficiency by a substantial amount (between 28 to 59%) (Wilson et al 1992). Photosynthetic efficiencies appear never to exceed about 22 % of the absorbed light energy in the 400 to 700 nm range, the maximum efficiency is obtained at relative low light intensities, not in brightest sunlight (Salisbury and Ross 1978). Considering the supply of light to available land area on which a crop is growing, the overall yield efficiencies are always much below 22% (Salisbury and Ross 1978). The use of CO2 in greenhouses can give light use efficiencies exceeding those of field crops (Wilson et al 1992). Glasshouse crops with CO2 enrichment achieve maximum efficiency of light energy utilization between 12-13% (Wilson et al 1992). The ability of plants to utilize CO2 is dependent upon the presence of light, for this reason it is only useful to supplement CO2 during the daylight hours (Styer and Koranski 1997). The key enzyme for CO2 fixation is rubisco (Tremblay and Gosselin 1998). The activity of rubisco depends on the ratio of the O2 and CO2 concentration in the atmosphere (Tremblay and Gosselin 1998). The major effect of CO2 enrichment is the shift in balance in the O2 and CO2 ratio which improves the activity of rubisco (Tremblay and Gosselin 1998). The effect is just as important at low as at high light levels since the percentage effect on relative growth rate is about the same over a range of light levels (Tremblay and Gosselin 1998). Transpiration rates are reduced under CO2 enrichment conditions by 34%. Increased net leaf photosynthesis rate and decreased transpiration rate under CO2 enrichment is well documented. One of the most important effects of CO2 enrichment is the increased water use efficiency (Tremblay and Gosselin 1998). The technique of enriching the greenhouse atmosphere with CO2 to maximize yield is standard practice (Slack et al 1988, Nederhof et al 1992, Rijkdijk and Houter 1993). The largest increase in growth rate achieved with CO2 enrichment is obtained with high light intensities. A high CO2 concentration may partially compensate for low light levels (Fierro et al 1994). There is

obviously a potential for synergism between CO2 and light, however the relationship between CO2 and light conditions may be relatively loose (Tremblay and Gosselin 1998). When greenhouse ventilation rates are high, the cost of CO2 supplementation can rise steeply. This is particularly so with a ventilation regime where ventilation is triggered at temperatures between 19 - 21 °C (Slack et al 1988). Investigations into delaying ventilation to increase the cost effectiveness of CO2 supplementation have shown that the amounts of CO2 supplied to the greenhouse could be reduced by 23 to 35% while still maintaining the CO2 content of the greenhouse atmosphere above ambient CO2 concentrations (Slack et al 1988). Delaying ventilation to conserve CO2 resulted in higher greenhouse temperatures with fruit temperatures exceeding 30 °C. However, total marketable yield fell by 11% and the proportion of fruit graded as Class 1 was reduced by 20% on average (Slack et al 1988). The best advice for CO2 supplementation under high ventilation rates is to maintain the CO2 concentration at or just above the normal ambient level of approximately 350 ppm (Slack et al 1988). This is a highly efficient way of using CO2 supplementation. Maintaining the CO2 concentration at the same level as ambient, there can be no net exchange of CO2 with the outside air through leakage or ventilation (Slack et al 1988). For practical purposes, the input of CO2 is therefore equal to that being assimilated by the crop during photosynthesis, i.e. the utilization of supplementary CO2 is totally efficient (Slack et al 1988). The main point being that ventilation and economical CO2 enrichment may be applied simultaneously. (Shina and Seginer 1989 Tremblay and Gosselin 1998). At higher temperatures, 25 °C, net photosynthesis begins to decline and the supplementation of CO2 above this temperature is not considered cost effective (Portree 1996). During longer periods of elevated CO2 the stomata remain partially closed and the reduction of transpiration may cause insufficient cooling, hence, heat damage to the leaves under conditions of intense light (Nederhoff et al 1992). However, the increased VPD associated with the higher temperatures has been shown to counteract the effect of stomatal closure due to CO2 supplementation (Nederhoff et al 1992). Since young plants grow nearly exponentially, they can benefit more from optimal growing conditions than mature plants (Tremblay and Gosselin 1998). Carbon dioxide enrichment results in heavier transplants and can be used to accelerate the growth, as well as improving the quality of the transplants (Tremblay and Gosselin 1998). Carbon dioxide may increase sugar translocation in the roots as well as facilitating the movement of nitrogen and carbon compounds directed towards the development of new roots (Tremblay and Gosselin 1998). In short, CO2 supplementation shortens the nursery period and results in sturdier, higher quality plants (Tremblay and Gosselin 1998).

Air Pollution in the Greenhouse

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Air pollutants can be a concern for greenhouse production. The incidence of air pollutant injury to plants is increasing as more growers use double plastic greenhouses, or other forms of greenhouse sealing to reduce energy loss (Blom 1998). Air pollutants can cause visible injury to the leaves, can reduce growth rates or both (Blom 1998). Tomatoes and cucumbers are particularly sensitive to air pollutant injury (Portree 1996). When considering the effects of greenhouse air pollutants ,it is important to remember that these pollutants pose significant health risks for people working the crops. Common pollutants are often by-products of combustion. Although sources of pollutants can be outside the greenhouse, a number of sources of pollutants can be found within the greenhouse. Pollutants can be produced by direct-fired heating units, gas supply lines or carbon dioxide generators that burn hydrocarbon fuels such as natural gas (Blom 1998). Significant sources of pollutants outside the greenhouse can include industrial plants or vehicle exhaust (Blom 1998).

Table 2: Maximum acceptable concentration (ppm)of some noxious gases for humans and plants

Gas Humans PlantsCarbon Dixoide (CO2) 5,000 4,500Carbon monoxide (CO) 47 100Sulfur dioxide (SO2) 3.5 0.1Hyfrogen sulfide (H2S) 10.5 0.01Ethylene (C2H4) 5.0 0.01Nitrous oxide (NO) 5.0 0.01 to 0.1Nitrogen dioxide (NO2) 5.0 0.2 to 2.0Adapted from Portree 1996

Air pollution from sources within the greenhouse commonly arise through cracked heat exchangers on furnaces or incomplete combustion in the furnace or CO2 generators. Heaters and generators should be checked at the beginning of the cropping season to ensure they are operating properly and complete combustion is occurring. The most common air pollutants resulting from incomplete combustion include nitrogen oxides, nitric oxide (NO) and nitrogen dioxide (NO2), sulfur dioxide (SO2), ethylene (C2H4), propylene (C3H6), ozone (O3), carbon monoxide (CO) and hydrogen sulfide (H2S) (Portree 1996, Blom 1998). Symptoms of air pollutant injury vary with the specific gases involved. The common symptoms of sulfur dioxide injury is characterized by severe leaf burn appearing withing 24 to 36 hours of exposure to high levels of the gas

(Blom 1998). There is a distinct line between the affected and unaffected areas on the leaves and young leaves are more susceptible to injury than mature leaves (Blom 1998). Symptoms of NO2 injury include darker than normal green leaves with downward curling leaf margins and dead areas on the leaves in severe cases (Blom 1998). Ethylene functions as a plant growth regulator, involved in seed germination, root development, flower development and leaf abscission (Salisbury and Ross 1978, Blom 1998). Ethylene injury can include a reduction in growth, shortening and thickening of stems and twisting of stems, as well as premature leaf and flower drop (Blom 1998). Propylene injury is similar to ethylene but usually occurs at concentrations 100 times higher than those for ethylene (Blom 1998). Ozone injury is characterized by mottling, necrotic flecking or bronzing necrosis of leaves, premature leaf drop and decreased growth (Blom 1998).

Growing Media

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Most commercial vegetable production greenhouses in Alberta use some form of "hydroponic culture". The term hydroponics essentially translates as 'water culture'. It is an advanced form of crop culture which allows for specific control of the delivery of nutrients to the plants (Salisbury and Ross 1978, Weiler and Sailus 1996). The term hydroponics can bring to mind a number of variations on the same theme. Hydroponic growing systems can include: substrate culture where the roots are allowed to grow in an inert or semi-inert media; solution culture where the roots are immersed in ponds of nutrient solution; NFT culture (nutrient film technique) where the roots are contained such that a thin film of nutrient solution constantly runs by the roots; and aeroponics where the root systems are suspended within an enclosed area and are misted with nutrient solution (Weiler and Sailus 1996). A general working definition of hydroponic culture that would include all of the above systems, is plant culture where the plants receive fertilizer nutrients every time they receive water. Using this working definition of hydroponics also leaves room for the inclusion of soil as a growing medium. However, soil culture is not widely practiced in commercial vegetable greenhouses in Alberta. The main reason for moving out of soil, into soilless culture, is to escape problems due to soil borne diseases (Maree 1994, Portree 1996) that can build-up in the soil used year after year. Soilless media such as rockwool and sawdust offer an initially disease-free growing medium. There are other advantages of moving the root system out of the soil and into confined spaces such as sawdust bags or rockwool slabs. The main advantages are realized in the improved management of watering and nutrition, topics which are discussed in more detail in following sections.

Media for Seeding and Propagation

Rockwool plugs are the most common media used for seeding. Rockwool is manufactured by subjecting rock mineral materials to very high temperatures and then spinning the materials into a fibre (Portree 1996). The plugs can be square (2 cm x 2 cm by 4 cm deep) and can come joined together as a rockwool "flat" that fit into standard 28 cm x 54 cm plastic seeding flats. As the seed germinates and the seedlings are ready for their first transplanting, the plugs easily separate from each other when the seedlings are transplanted into rockwool blocks. Rock wool blocks are typically around 10 cm x 10 cm by 8 cm deep, with a depression cut into the upper surface to receive the rockwool plug at the first transplanting. As the seedling continues to grow, the root system develops from the rockwool plug into the confines of the block. When the seedling is ready for transplanting into the main production greenhouse at "house set", the bottom of the rockwool block is placed in direct contact with the larger volume of growing media used in the production house.

Growing Media for the Production Greenhouse

The majority of Alberta's commercial greenhouse vegetable production is based on substrate culture where the plants are grown in sawdust or rockwool. These substrates contain practically nothing in the way of plant nutrients and serve as a substrate for the root system to anchor the plant. The growing media plays a significant role in defining the environment of the root system and allows for the transfer of water and nutrients to the plant. Typically, for sawdust culture, 2 or 3 plants are grown in 20 to 25 litre white plastic bags (white reflects more light) filled with spruce and/or pine sawdust. Rockwool culture uses approximately 16 litres of rockwool substrate for every 2 to 3 plants (Portree 1996). The sawdust bags or rockwool slabs are placed directly on the white plastic floor of the greenhouse. Sawdust is less expensive than rockwool in initial cost, however standard density rockwool slabs can be pasteurized and reused for up to three years (Maree 1994, Portree 1996). Sawdust is a waste product of the lumber milling process which is usually burned, so the use of sawdust as a growing media is an environmentally sound practice. For sawdust culture it is important to use a moderately fine sawdust, lumber mills in Alberta understand the sawdust requirements for plant production and will supply "horticultural grade" sawdust if they are made aware that the sawdust is to be used for plant culture. Using sawdust that is too fine will break down over the production season with resulting loss of airspace around the roots which can lead to root death (Benoit and Ceustermans 1994, Portree 1996). There is always some decomposition of the sawdust during the growing season (Benoit and Ceustermans 1994) which makes the product useful for further composting or adding to mineral soils to improve soil quality. Through the continued action of soil microbes the sawdust residue at the end of the cropping season is returned to the environment in an ecologically sound manner. The waste from sawdust culture is confined to the plastic bags themselves which are recovered when the sawdust bags are dumped and can be recycled where facilities exist.

Management of Irrigation and Fertilizer Feed

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

In hydroponic crop production systems the application of water is integrated with the application of the fertilizer feed. The management of fertilizer application to the plants is therefore integrated with the management of watering. The management of watering and nutrition is focused on the optimal delivery of water and nutrients over the various growth stages of the plant, through the changing growing environment over the production year, in order to maximize yield.

Management of Irrigation and Fertilizer Feed - Water Quality

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Plants are comprised of 80 to 90% water (Salisbury and Ross 1978) and the availability of adequate quality water is very important to successful crop production (Portree 1996, Styer and Koranski 1997). The quality of water is determined by what is contained in the water at the source; well, dugout, town or city water supply, and the acidity or alkalinity of the water. Water is a solvent, and as such, it can contain or hold a certain quantity of soluble salts in solution. Fertilizers, by their nature, are soluble salts, and growers dissolve fertilizers in water to obtain nutrient solutions in order to provide the plants with adequate nutrition. Prior to using any source of water for crop production it is important to have it tested for quality. Water quality tests determine the amount of various salts commonly associated with water quality concerns. The maximum desirable concentrations, in parts per million (ppm), for specific salt ions in water for greenhouse crop production are presented in table 3. Parts per million are one unit of measurement of the amount of dissolved ions, or salt in water, and are also used to measure the level of dissolved fertilizer salts in nutrient solutions. The level of nutrients as dissolved ions in water can also be reported in milligrams/Litre of solution. There is a direct relationship between milligrams/Litre (mg/L) and ppm, where 1 mg/L = 1 ppm. Another common unit of measure for dissolved fertilizer salts is the millimole (mM), the concept of millimoles and the relationship between millimoles and ppm is explained in the special topic section.

Figure 17. The relationship between common units ofmeasurement for electrical conductivity (E.C.)1 mmho/cm = 1 mS/cm = 1000 microsiemens/cm

Table 3: The maximum desirable concentrations, in parts per million (ppm),

for specific salt ions in water for greenhouse crop production.

Element Maximum desirable (ppm)

Nitrogen (NO3 - N) 5Phosphorus (H2PO4 - P) 5Potassium (K+) 5Calcium (Ca++) 120Magnesium (Mg++) 25Chloride (Cl-) 100Sulphate (SO4

--) 200Bicarbonate (HCO3

-) 60Sodium (Na++) 30Iron (Fe+++) 5Boron (B) 0.5Zinc (Zn++) 0.5Manganese (Mn++) 1.0Copper (Cu++) 0.2Molybdenum (Mo) 0.02Fluoride (F-) 1

pH 75

E.C. 1Water quality tests will also report the pH, the acidity or alkalinity of the water. Once the source of water has been determined as suitable for greenhouse crop production it is also important to have the water tested routinely to ensure that any fluctuations in quality that may occur does not compromise crop production. Electrical Conductivity of Water Water quality analyses also report the electrical conductivity or E.C. of the water. The ability of water to conduct an electrical current is dependent of the amount of ions or salts dissolved in the water. The greater the amount of dissolved salts in the water, the more readily the water will conduct electricity. Electrical conductivity is an indirect measurement of the level of salts in the water and can be a useful tool for both determining the general suitability of water for crop production, and for the ongoing monitoring of the fertilizer feed solution. Using electrical conductivity as a measure to maintain E.C. targets in the nutrient solution and the root zone can be used as a management tool for making decisions regarding the delivery of fertilizer solution to the plants. Electrical conductivity is measured and reported using a number of measurement units including millimhos per centimeter (mmhos/cm), millisiemens per centimeter (mS/cm) or microsiemens per centimeter. Water

suitable for greenhouse crop production should not have a E.C. in excess of 1.0 mmhos/cm. pH The relative acidity and alkalinity of the water is expressed as pH (Styer and Koranski 1997), and is measured on a scale from 0 to 14. The lower the number, the more acidic the water or solution, the higher the number the more alkaline (Boikess and Edelson 1981). The pH scale is a logarithmic scale, meaning that every increase of one number ie. 4 to 5, represents a ten times increase in alkalinity. Conversely, every single number decrease, ie. 5 to 4, represents a ten times increase in acidity. Most water supplies in Alberta are alkaline, with typical pH levels of 7.0 to 7.5. Alkalinity of the water increases with increasing levels of bicarbonate. The pH measurement reflects the chemistry of the water and nutrient solution. The pH of a fertilizer solution has a dramatic determining effect on the solubility of nutrients, how available the nutrients are to the plant (Portree 1996, Styer and Kornaski 1997). The optimum pH of a feed solution, with respect to the availability of nutrients to plants, falls within the range of 5.5 to 6.0 (Portree 1996). The pH of a solution can be adjusted through the use of acids such as phosphoric or nitric acid, or potassium bicarbonate, depending on which direction the feed solution needs to be adjusted. When acids or bases are used to adjust the pH of the feed solution, the nutrients added by the acid; nitrogen, phosphorus, must be accounted for when the feed solution is calculated. Most water supplies in Alberta are basic in pH and require the use of acid for pH correction. The amount of acid required to adjust the pH is usually dependent on the bicarbonate (HCO3-) level in the water. The amount of bicarbonate in the water supply can be determined by a water analysis, and is reported in ppms. A good target pH for nutrient feed solution is 5.8, and as a general rule this pH corresponds to a bicarbonate level of about 60 ppm. If the incoming water has, for example, a pH of 8.1 and a bicarbonate level reported at 207 ppm, 207 ppm - 60 ppm = 147 ppm that needs to be neutralized by acid to reduce the pH from 8.1 to 5.8. In order to neutralize 61 ppm, or 1 milliequivalent, of bicarbonate it takes about 70 ml of 85% phosphoric acid, or about 84 ml of 67% nitric acid per 1000 litres of water. In order to neutralize 147 ppm of bicarbonate:

Using 85% phosphoric acid.

140 / 61 = 2.3 milliequivalents of bicarbonate to be neutralized2.3 milliequivalents x 70 ml of 85% phosphoric acid for each milliequivalent= 2.3 x 70 ml = 161 mls of 85% phosphoric acid for every 1000 litres of water.

Using 67% nitric acid.

2.3 milliequivalents of bicarbonate to be neutralized.2.3 milliequivalents x 76 ml per milliequivalent= 2.3 x 76 ml = 175 mls of 67% nitric acid for every 1000 litres of water

These calculations have to be made for each water sample based on the results of water a analysis reporting the level of bicarbonates. In addition to phosphoric and nitric acid, sulfuric and hydrochloric acids can also be used to adjust the pH of the water down. Acids are corrosive. Special care and attention must be used when handling them for pH correction. The common acids used to lower the pH are phosphoric acid (85%) and nitric acid (67%), of these two, nitric acid is the most corrosive (Styer and Koranski 1997) and must be handled very carefully. Acid resistant safety glasses, rubber gloves and a rubber apron should be the minimum safety equipment used when handling acids.

Management of Irrigation and Fertilizer Feed - The Mineral Nutrition of Plants

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

In order to support optimum growth, development and yield of the crop, the fertilizer feed solution has to continually meet the nutritional requirements of the plants. Although the mineral nutrition of plants is complex, experience in crop culture has determined basic requirements for the successful hydroponic culture of plants. There are 13 mineral elements that are considered essential for plant growth. Water (H2O) and carbon dioxide (CO2) are also necessary for plant growth and supply hydrogen, carbon and oxygen to the plants bringing the total to 16 essential elements (Salisbury and Ross 1978).

Table 4: The essential mineral elements for plants

Element Symbol Type Mobility in Plant Symptoms of Deficiency

Nitrogen N macronutrient mobile Plant light green, lower (older) leaves yellow.Phosphorus P macronutrient mobile Plant dark green turning to purple.Potassium K macronutrient mobile Yellowish green margins on older leaves.Magnesium Mg macronutrient mobile Chlorosis between the veins on older leaves

first, turning to necrotic spots, flecked appearance at first.

Calcium Ca macronutrient immobile Young leaves of terminal bud dying back at tips and margins. Blossom end rot of fruit (tomato and pepper).

Sulfur S macronutrient immobile Leaves light green in color.

Iron Fe micronutrient immobile Yellowing between veins on young leaves (interveinal chlorosis), netted pattern.

Manganese Mn micronutrient immobile interveinal chlorosis, netted patternBoron B micronutrient immobile Leaves of terminal bud becoming light green

at bases, eventually dying. Plants "brittle."Copper Cu micronutrient immobile Young leaves dropping, wilted appearance.Zinc Zn micronutrient immobile interveinal chlorosis of older leaves.

Molybdenum Mo micronutrient immobile Lower leaves pale, developing a scorched appearance.

A criterion to determine whether an element is essential to plants is if the plant cannot complete its life cycle in the complete absence of the element (Salisbury and Ross 1978). In addition to the essential elements there are other elements, although not necessarily considered universally essential, which can affect the growth of plants. Sodium (Na), chloride (Cl) and silicon (Si) are in this category, all three of these nutrients either enhance the growth of plants, or are considered essential nutrients for some plant species (Wilson and Loomis 1967, Salisbury and Ross 1978, Styer and Koranski 1997). The essential nutrients can be grouped into two categories reflecting the quantities of the nutrients required by plants. Macronutrients or major elements, are required by plants in larger quantities, when compared to the amounts of micronutrients, or trace elements required for growth (Salisbury and Ross 1978). Another useful grouping of the mineral nutrients is based on the relative ability of the plant to translocate the nutrients from older leaves to younger leaves (Salisbury and Ross 1978). Mobile nutrients are those which can readily be moved by the plant from older leaves to younger leaves, nitrogen is an example of a mobile nutrient (Salisbury and Ross 1978). Calcium is an example of an immobile nutrient, one which the plant is not able to move after it has initially been translocated to a specific location (Salisbury and Ross 1978). The discussion of plant nutrients as elements does not allow for a more complete discussion of how plants access the elements from the root environment, and how hydroponic growers ensure that their crop plants are adequately supplied with nutrients. The term "element" can be defined as a substance that cannot be broken down into simpler substances by chemical means, the basic unit of an element is the atom (Boikess and Edelson 1981). With the simplest, or purest form of plant nutrients being the atom, nutrients are not often available to plants in their purest form. Pure nitrogen is an example of a nutrient element represented by its atom. When the atoms of different elements combine, they can form other substances which are based on a particular combination of atoms, substances based on molecules. Nitrate (NO3-), is a molecule based on nitrogen and oxygen atoms, nitrate is absorbed by plant roots as a source of nitrogen. Nitrate is an "available" form of nitrogen. The nitrate molecule has an overall negative charge, which

causes the molecule to be fairly reactive chemically, and therefore more available. The availability of nutrient elements to plants is generally based on the existence of the nutrient element as a charged particle, either a charged atom or charged molecule. An atom or molecule that carries an electric charge is called an ion, and positively charged ions are called cations, while negatively charged ions are called anions. The nitrate molecule (NO3-) is an anion, the iron atom can exist as the Fe+2 (ferrous) or Fe+3 (ferric) cations (Boikess and Edelson 1981). Plants are able to acquire the essential mineral elements via the root system utilizing the chemical properties of ions, particularly that to acquire negatively charged anions, the plant roots have sites that are positively charged. The plant is also able to attract positively charged cations to negatively charged sites on the root. Water is a very important component in the acquisition of nutrient elements by the plants as the nutrient ions only exist when they are in solution, when they are dissolved in water. As solids, the ions generally exist as salts, a salt can be defined as any compound of anions and cations (Boikess and Edelson 1981). In the absence of water, the nutrient ions form compounds with ions of the opposite charge. Anions combine with cations to form a stable solid compound. For example, the nitrate anion (NO3-) commonly combines with the calcium (Ca+2) or potassium (K+) cations forming the larger calcium nitrate Ca(NO3)2 potassium nitrate (KNO3) salt molecules. As salts are added to water, they dissolve, or dissociate into their respective anion and cation components. Once in solution they become available to plants. An important point to remember is that different salts have different solubilities, that is, some salts readily dissolve in water (highly soluble), and some salts do not. Calcium sulfate (CaSO4) is a relatively insoluble salt and would be a poor choice as a fertilizer because very little of the calcium would go into solution as the calcium cation (Ca++) and be available to plants. Fertilizer salts, by their very nature, are useful because they go into solution readily. In hydroponic culture, greenhouse growers formulate and make a water based nutrient solution by dissolving fertilizer salts. In addition to existing as salts, some of the micronutrients; iron, zinc, manganese and copper, exist in chelates. A chelate is a soluble product formed when certain atoms combine with certain organic molecules. The sulphate salts of iron, zinc, manganese and copper are relatively insoluble and chelates function to make these mineral nutrients more readily available in quantity to the plants (Boikess and Edelson 1981).

Management of Irrigation and Fertilizer Feed - Fertilizer Feed Programs

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Fertilizer nutrient solutions are formulated to meet the needs of the plants using a combination of component fertilizer salts. The amounts of the various fertilizers used are dependent on target levels which have been determined to be optimal for the crop in question. Although there is considerable similarity between fertilizer programs for the various vegetable crops, there can be some differences reflecting the different requirements of the crop. In any event, when mixing fertilizer solutions, only high quality water-soluble fertilizers should be used.

Table 5: Forms of mineral nutrient elements that are commonly available to plantsElement Symbol Available as Symbol

MacronutrientsNitrogen N Nitrate ion

Ammonium ionNO3

-

NH4+

Phosphorus P Monovalent phosphate ionDivalent phosphate ion

H2PO4-

HPO4-2

Potassium K Potassium K+

Calcium Ca Calcium ion Ca+2

Magnesium Mg Magnesium ion Mg+2

Sulfur S Divalent sulfate ion SO4-2

Chlorine Cl Chloride ion Cl-

MicronutrientsIron Fe Ferrous ion

Ferric ionFe-2

Fe-3

Manganese Mn Manganous ion Mn+2

Boron B Boric acid H3BO4

Copper Cu Cupric ion chelateCuprous ion chelate

Cu+2

Cu+

Zinc Zn Zinc ion Zn+2

Molybdenum Mo Molybdate ion MoO4-

The required nutrient levels, or target nutrient levels of the various essential elements are often expressed as the desired parts per million (ppm) in the final nutrient solution. The recommended nutrient fertilizer feed targets for greenhouse peppers are listed in table 6. Even though all thirteen mineral elements are essential for plant growth and development, nutrient targets for sulfur and chlorine are not listed. The reason for this is adequate amounts of sulfur are obtained from the use of sulfate fertilizers, potassium sulfate or magnesium sulfate. Chloride is assumed to be present in adequate amounts as a contaminant in a number of fertilizers. As the purity of fertilizers has improved, growers will have to pay more attention to ensuring these other elements, particularly chloride, are present in adequate amounts. Once the recommended nutrient targets are known, calculations are made to determine how much of each fertilizer is required in order to meet them.

In order to make these calculations some other basic information is required: 1. The volume of water that will be used to make the feed solution. 2. The types of fertilizers that are available, and the relative amounts of each

nutrient present in the fertilizer.

When considering what volume of water to use for the nutrient solution it is first important to understand the delivery of the nutrient solution to the plants as discussed earlier in "Irrigation and fertilizer feed systems." Every greenhouse must be able to supply water and nutrients on an ongoing basis. During hot, dry Alberta summers, mature pepper plants can use approximately 3.5 to 4.0 litres of water per plant per day, cucumbers can require over 6 litres, tomatoes up to 3 litres. This water always contains fertilizer which is added as the water comes into the greenhouse and before it is pumped to the plants. There are a number of variations on the theme, but some form of fertilizer injection system is used in all commercial scale greenhouses.

Table 6: Nutrient feed targets (ppm) for greenhouse sweet peppers

grown in sawdust.Nutrient Target (ppm)Nitrogen 200Phosphorus 55Potassium 318Calcium 200Magnesium 55Iron 3.00Manganese 0.50Copper 0.12Molybdenum 0.12Zinc 0.20Boron 0.90

Feed Targets and Plant Balance The first approach to altering the feed solution in response to a crop that is overly vegetative is to increase the feed E.C. to direct the plants to become more generative and set and fill more fruit. The feed EC can be increased from 2.5 mmhos to approximately 3.0 mmhos over the course of a few days. Dialing up the feed E.C. increases the absolute amounts of fertilizer nutrients in the feed but does not affect the ratio of the nutrient levels with respect to one another. Increasing the feed E.C. increases the level of fertilizer salts in the root zone, increasing the stress on the plant as it becomes more difficult for the plant to take up water. The plant responds to the stress by putting

more emphasis on fruit production, a stressed plant begins preparations for the end, by trying to ensure that the next generation will carry forward. The fruit holds the seed, and in plant terms, developing fruit means that the next generation will survive and carry on. Now plants don't think these things out, but stressing the plant does direct the plant to set more fruit. There is a limit to how far growers can go with this as a successful crop requires having enough vegetative growth to continually fill a high volume of fruit consistently throughout the season. There is another option available for affecting the vegetative/generative balance of the plants, through manipulation of the nutrient ratios, particularly the nitrogen-potassium ratio.

Typical absolute value, and relative ratio targets for N, K and Ca in vegetable feed

programs (E.C. of 2.5 mmhos) for Southern Alberta production conditions

CropNutrient Targets (ppm)

Nutrient Ratio

N K Ca N K Cacucumber 20

0300

173 1.00 1.51 0.86

pepper 214

318

200 1.00 1.48 0.93

The N:K ratios presented in the table, are all about 1:1.5, increasing the level of potassium, with respect to nitrogen, and increasing the ration to 1:1.7 will direct the plant to be more generative. The reason for this is that nitrogen promotes vegetative growth while potassium promotes mature growth, generative growth. Calcium is also important for promoting strong tissues, fruit, and mature growth. Shifting the feed program to favor potassium over nitrogen will direct the plant to be generative. Calcium is important in the equation in that it should always be approximately equal to the amount of nitrogen. A N:Ca ration of 1:1, works for both tomatoes and peppers, while a N:Ca ratio of 1:0.85 has shown to work well for cucumbers. Changes to the N:K ratio should be made carefully, the above ratios come from the feed programs of successful Alberta growers and can serve as a guide. The place to start is to determine the ratios in the current feed program and examine the performance of he crop. If it is determined that there is room for improving the balance of the plants, alterations in the nutrient ratios can be undertaken. Always be aware that many factors influence plant balance: day/night temperature split, 24 hour average temperature, relative humidity and watering. These factors should be optimized before feed ratios are changed. You have to know where the crop is in order to make sound decisions on where it should be, and how to get there.

Due to the large volumes of fertilizer feed solution that can be required daily, it is impractical to make the fertilizer feed on a day to day basis. Instead, the required fertilizers can be mixed in a concentrated form, usually 100 to 200 times the strength that is delivered to the plants. Injectors or ratio feeders are then used to "meter-out" the correct amount of fertilizer into the water which make up the nutrient solution going to the plants. By using concentrated volumes of the fertilizer feed held in "stock tanks" growers are able to reduce the number of fertilizer batches they have to make. Depending on the number of plants in the crop, the size of the stock tanks, and the strength of the concentrate, growers may only have to mix fertilizer once every 2 to 4 weeks.

Management of Irrigation and Fertilizer Feed - Fertilizer Feed Programs

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Designing a fertilizer feed program

The design of a fertilizer feed program is a relatively straight forward process once the nutrient target levels are decided and basic information about the water quality, feed delivery system, and component fertilizers are known. Fertilizer targets and the component fertilizers used to make the fertilizer solution can change over the course of the year depending on the crop and the knowledge of the grower. Often the changes are slight adjustments in the relative proportion of the macronutrients to one another, particularly the nitrogen:phosphorus:potassium (N:P:K) ratio. Changes can also include the addition of alternate forms of a nutrient in question, a common example is the use of ammonium nitrogen (NH4 - N) in addition to nitrate nitrogen (NO3 - N) during the summer months. Ammonium nitrate is the common source of ammonium nitrogen, which is a more readily available form of nitrogen that works to promote vegetative growth. During the summer months a target of approximately 17 ppm of ammonium nitrogen is recommended to help optimize plant balance and crop production.

Moles and millimoles in the greenhouse; Just another couple of rodents?? Just when you thought you had all your rodent problems under control, some greenhouse vegetable growers have been concerned about millimoles and moles. Not to worry, these growers are not referring to four legged moles. Rather they are using another unit of measure to discuss fertilizer feed targets and root zone targets. So, what exactly is a millimole? A millimole is one thousandth of a mole, and a mole is defined as the amount of a substance of a system which contains

as many elementary entities as there are atoms in exactly 12 grams of 12 C (Carbon 12). Now, you were probably expecting that a definition would help clarify the situation, isn't that what definitions are supposed to do? The concept of the mole has come out of stoichiometry, that branch of chemistry which studies the quantities of reactants and products in chemical reactions. Now a lot of chemists and physicists have argued for a long time over how to measure the masses of individual elements (some of those same elements that growers feed their crops in fertilizer feed solutions) and in 1961 they settled on using the mole. A good way to understand what a mole is and why to use it is to related it to the concept of a dozen. We understand that a dozen is twelve of something, be it cucumbers, eggs or whatever. A mole is 6.02 x 1023 of some entity, and chemists usually refer to actual molecules of a substance when they talk about moles, although you could have a mole of eggs or a mole of cucumbers. You would be quite the grower to grow a mole of cucumbers, tomatoes or peppers. The number 6.02 x 1023 , which in long hand is 602 000 000 000 000 000 000 000, is called Avogadro's number after the nineteenth century chemist who did some pioneering work on gases and was largely ignored for his trouble. The lesson here is that if you do something great and are not feeling appreciated for the greatness, someone, far into the future may name a big number after you. Moles do relate to parts per million (ppm), they are both ways to measure how much of a given nutrient we are dealing with in a fertilizer feed sample, leachate or tissue sample. The difference is that ppm is a measure of mass (e.g. 1 ppm = 1 milligram/litre) and moles measure amounts. One mole of any substance contains Avogadro's number of entities or basic units. Those entities, as mentioned earlier, can be atoms or molecules or whatever you want. When we talk about one mole of nitrate nitrogen, NO3, we are referring to 6.02 x 1023 molecules of NO3, because the basic NO3 entity is made up of one atom of nitrogen (N) and three atoms of oxygen (O). If we are talking about a mole of iron, Fe, we are talking about atoms, because the basic entity of iron is the iron atom. All atoms and molecules have different basic weights, some being heavier than other. If we talk about 1 ppm of NO3 versus 1 ppm of Fe, we are talking about the same mass of each, i.e., 1 milligram/litre. However, there will be a different number of basic entities or moles of NO3 and Fe in a solution which contains 1 ppm each of NO3 and Fe. Now, we are getting close to being able to convert ppm to moles or millimoles, but we will first consider the concept of atomic and molecular weights. The atomic weights of all the elements can be found on the periodic table, that handy chart that we carried with us throughout all our chemistry classes. The atomic weights of the elements are given in grams per mole. The molecular weight of oxygen is 16 grams/mole, this means that 6.02 x 1023 atoms of oxygen weights 16 grams. One mole of nitrogen weighs 14 grams. By combining all the atoms which make up molecules we can arrive at the molecular weights. Therefore, the molecular weight of NO3 would equal 14 + 3(16) grams/mole or 62 grams/mole. One last thing to remember is that

moles are related to millimoles the same way that grams are related to milligrams. So if moles are related in the range of grams, millimoles are in the range of milligrams. We know that 1 ppm is equal to 1 milligram/litre, so to convert ppm to millimoles you divide ppm by the molecular weight of the element you are working with. For example:

1 ppm of NO3 = 1 mg/litre

1 mg/ litre of NO3 / 62 mg/mole = 0.016 millimoles of NO3 in one litre

1 ppm of Fe = 1 mg/litre

1 mg/litre of Fe / 56 mg/millimole = 0.018 millimoles of Fe in one litre.

1 ppm of magnesium (Mg) = 1 mg/litre

1 mg/litre of Mg / 24 mg/millimole = 0.041 millimoles of Mg in one litre.

As these examples show, a solution containing 1 ppm of various elements or molecules will contain different mole or millimole amounts of these same elements.

To convert millimoles to ppm:

ppm = millimoles/litre x molecular weight (mg/millimole)

Example:

ppm NO3 = 0.016 millimoles of NO3 in one litre x 62 mg/millimole

= 1 ppm NO3

Once you can work back and forth between ppms and millimoles, you might be asking if there is any benefit to working in millimoles rather than ppm. If you are comfortable working with ppms and you are comfortable with designing and managing your fertilizer feed programs in ppms, stick to what you know. However, if you want to be working with actual amounts of atoms and molecules of the nutrients you are feeding then you may want to work with millimoles. Whatever the case, with a little practice you can work with either unit. Reference: Boikess, R.S. and E. Edelson, 1981. Chemical Principles, Second Edition. Harper and Row, New York.

Calculating the required amounts of the various fertilizers is dependent on the volume of water to be used. This is determined by the volume of the stock tank (e.g. 200 litres) multiplied by the injection ratio (e.g. 100:1 or

200:1). For example, using a 200 litre fertilizer concentrate stock tank, and a 200:1 injection ratio, the volume of water that will be used to calculate the amount of fertilizer to add will be:

200 litres (stock tank volume) x 200 (injector ratio) = 40,000 litresThe following calculations will be based on 200 litre stock tanks and a 1:200 injection ratio.

Management of Irrigation and Fertilizer Feed - Fertilizer Feed Programs

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Accounting for the nutrients present in the raw water

Assuming the water quality analysis has determined that the water is suitable for greenhouse crop production, the first step is to account for the nutrients that are already contained in the water. This information comes directly from the water analysis report.

Management of Irrigation and Fertilizer Feed - Fertilizer Feed Programs

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Accounting for the nutrients provided by the pH adjustment of the water

Next determine if the pH needs adjusting, and if so, the amount of acid (or base) required to meet the target pH of 5.8. Once the amount of acid to be added has been determined, the levels of nutrients present in the acid have to be accounted for. Using the example in the previous section, where it was determined that 161 ml of 85% phosphoric acid would be required to adjust the pH from 8.1 to 5.8 for every 1,000 litres of water, the amount of acid required for 40,000 litres would be (161 ml/1,000 litres x 40,000 litres =) 6,440 mls. Knowing the volume of acid required, and the specific gravity of the acid, it is possible to calculate the weight of acid that will be used.

Table 7: The specific gravity of 85% phosphoric and 67% nitric acid.Phosphoric acid (85%) 1.41 grams/mlNitric acid (67%) 1.28 grams/ml

6,440 mls (85% phosphoric acid) x 1.41 grams/ml = 9,080 grams of phosphoric acid.

Having the weight of the acid, it is now possible to determine the amount of phosphorus contributed to the pH-adjusted water by 85% phosphoric acid. One more piece of information is required, phosphoric acid contains 32 % available phosphorus. This is also referred to as the fertilizer grade of the acid. Now, using the following formula:

(Formula 1) * from Mirza and Younus, 1994

ppm = grams of acid x grade of acid x 10litres of water

the amount of phosphorus (in ppm) contributed by 7,857 grams of 85% phosphoric acid

= 9,080 grams x 32% x 1040,000

= 73 ppm of phosphorus, actual "P".This same sequence of calculations can be used to determine the amount of nitrogen contributed if 67% nitric acid was used. In this example 49 ppm of nitrogen would be contributed if 67% nitric acid was used.

Management of Irrigation and Fertilizer Feed - Fertilizer Feed Programs

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Determining the required amounts of the various fertilizers necessary to meet the feed targets

For the purposes of this discussion of designing a fertilizer program, only component fertilizers will be considered, a list of the common component fertilizers for greenhouse crop production is presented in table 9. The fertilizers are identified by their chemical name, and their fertilizer number designation, ie. 0-53-35 for monopotassium phosphate. The "grade" of the fertilizer with respect to the different nutrients supplied by the fertilizer, is also provided. It is important to know that the three number designation of the fertilizer represents the percentages or grade of nitrogen (N), phosphorus (P) and potassium (K), in that order, that is present in the fertilizer. However, it is very important to note when the percentages for phosphorus and potassium are used, the number on the bag represents the percentages of phosphate (P2O5) and potash (K2O) and not actual phosphorus and potassium. Phosphate is only 43% actual phosphorus and potash is only 83% actual potassium. For this reason, monopotassium phosphate, 0-53-35, is listed as containing 23% phosphorus (53% x 0.43 = 23%), and 29% potassium (35% x. 0.83 = 29%).

Table 8: Fertilizer "upgrades" of phosphoric and nitric acidPhosphoric acid 32% available phosphorus

(PO4-P)Nitric acid 22% available nitrogen

(NO3-N)Blended, or premixed fertilizers are also used by some growers. A common premixed fertilizer is 20-20-20. If these fertilizers are used it is important to account for all the nutrients provided in the fertilizer, both macro and micronutrients. As well, although the fertilizer 20-20-20 contains 20% nitrogen, for the purposes of calculating actual phosphorus (P) and actual potassium (K), 20-20-20 should actually be considered as 20-8.6-16.6. In determining the amount of fertilizer to add, it is important to remember that as salts, fertilizers often contain more than just one plant nutrient. For example, calcium nitrate (Ca(NO3)2) provides both calcium and nitrogen. Calcium nitrate is commonly used in commercial vegetable greenhouses as the only source of calcium. The amount of calcium nitrate added depends on how much is required to meet the calcium target. However since nitrogen is also present in calcium nitrate, it is important to keep track of how much nitrogen is contributed. After all, there is also an optimum target for nitrogen. Calcium nitrate is 19 % calcium and 15.5 % nitrogen so for every 100 grams of calcium nitrate there will be 19 grams of calcium and 15.5 grams of nitrogen. The percentage of the relative nutrient components of a fertilizer is also sometimes referred to as the "grade." As the fertilizer calculations are made, an ongoing tally is kept on what nutrients are being supplied by the various fertilizers until all the feed targets have been met. With the information of stock tank size, injector ratio, and the nutrients contributed by each fertilizer, the same relatively simple formula [Formula 1 (Mirza and Younus, 1994)] can be used to determine the amount of each fertilizer required to meet the parts per million (ppm) feed targets of the essential nutrients.

grams of fertilizer required = ppm desired x litres of watergrade of fertilizer x 10

This formula can be rearranged to calculate ppm if the amount of fertilizer added is known.

(Formula 2) * from Mirza and Younus, 1994

ppm = grams of fertilizer x grade of fertilizer x 10litres of water

Continuing with the example, using 200 Litre stock tanks, a 200:1 injector ratio, meeting a calcium target in the nutrient solution of 180 ppm, and obtaining all the calcium from calcium nitrate. The formula can be used to determine the amount of calcium nitrate required to meet the calcium target,

as well as determining the levels of nitrogen (in ppm) contributed by the calcium nitrate.

Calcium required = 180 ppm, from calcium nitrate, 19 % calcium, 15.5 % nitrogen.

grams of calcium nitrate required = 180 ppm x (200 x 200) litres of water19% x 10

=180 ppm x 40,000 litres of water190

=37,894 grams

=37.9 kilograms

The amount of nitrogen contributed:

ppm of nitrogen = 37,894 grams x 15.5% x 1040,000 litres

=146.8 = 147 ppm of nitrogenBy repeating this type of calculation using the various component fertilizers, including the micronutrient chelates, all the individual nutrients coming from each fertilizer can be accounted for, until all the nutrient targets are met and balanced in the final feed program.

Table 9. Some component fertilizers for formulating nutrient feed programs for hydroponic greenhouse

vegetable crops.Macronutrients Fertilizer Nutrients

Nitrogen Calcium nitrate15.5-0-0

15.5% nitrogen (NO3-N)19% calcium

Potassium nitrate13-0-44

13% nitrogen (NO3-N)37% potassium

Ammonium nitrate34-0-0

17% nitrogen (NO3-N)17% nitrogen (NH4-N)

Phosphorus Monopotassium phosphate0-53-44

23% phosphorus29% potassium

Potassium Potassium nitrate13-0-44

37%potassium13% nitrogen (NO3-N)

Potassium sulfate0-0-50

41.5% potassium17% sulfur

Monopotassium phosphate0-53-44

23% phosphorus29% potassium

Potassium chloride0-0-60

49% potassium26% chlorine

Calcium Calcium nitrate15.5-0-0

19% calcium15.5% (NO3-N)

Calcium chlorideCaCl2-2H2O

27% calcium48% chlorine

Magnesium Magnesium sulfateMgSO4-7H2O

10% magnesium13% sulfur

Magnesium nitrateMg(NO3)2-6H2

10% magnesium11% nitrogen (NO3-N)

Sulfur Magnesium sulfateMgSO4-7H2O

10% magnesium13% sulfur

Potassium sulfate0-0-50

41.5% potassium17% sulfur

Chlorine Calcium chlorideCaCl2-2H2O

27% calcium48% chlorine

Potassium chloride0-0-60

49% potassium26% chlorine

MicronutrientsIron Iron chelate 13% ironManganese Manganese chelate 13% manganeseCopper Copper chelate 14% copperMolybdenum Sodium molybdate 39% molybdenumBoron Borax 15% boron

Management of Irrigation and Fertilizer Feed - Rules for mixing fertilizers

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Once the amounts of the various fertilizers have been determined, the next step is to mix the fertilizers in the stock tanks. Most commercial vegetable greenhouses use a two stock tank system for mixing fertilizers, although some systems involve three stock tanks with the third tank containing the acid or bicarbonate for pH adjustment. Before mixing fertilizers ensure that a dust mask and gloves are worn to avoid inhaling the fertilizer dusts or contacting the fertilizer concentrates. The first rule in mixing fertilizers is to always use high quality, water soluble "greenhouse grade" fertilizers. Second, when working with stock tank concentrates, never mix calcium containing fertilizers (e.g. calcium nitrate) with any fertilizers containing phosphates (e.g. monopotassium phosphate) or sulfates (e.g. potassium sulfate, magnesium sulfate). When fertilizers containing calcium, phosphates or sulfates are mixed together as concentrates the result is insoluble precipitates of calcium phosphates and calcium sulfates. Essentially the calcium combines with the phosphate or sulfate in the solution and comes out of the solution as a solid. This solid forms a "sludge" at the bottom of the fertilizer tank which can plug the irrigation lines. This reaction between calcium, phosphate and sulfate can be avoid if a 1-times strength fertilizer is being mixed, as it is considerably more dilute. However, mixing fertilizers to make a 1-times strength fertilizer solution is impractical for a commercial greenhouse operation as it would necessitate that someone be mixing fertilizers almost continuously. The third rule for mixing fertilizers is to dissolve the fertilizers for each tank together in hot water. The components of tank 1 are dissolved togther as are the components of tank 2. The micronutrients are added to the tanks when the solution is warm, not hot. Fourth, is to continually agitate the solution in the stock tanks as the fertilizers are being added. Using the two-tank stock tank system, the fertilizers should be mixed as follows Tank A Tank Bcalcium nitrate potassium nitrate (one half the total amount)potassium nitrate (one half the total amount) magnesium sulfateiron chelate monopotassium phosphate

potassium sulfatemanganese chelatezinc chelatecopper chelatesodium molybdateboric acid

If other fertilizers are used, ensure that mixing calcium containing fertilizers with phosphate or sulfate containing fertilizers is avoided. Generally other nitrate fertilizers can be added to the "A" tank, while with all others mixed in the "B" tank. Note that iron is always added to the "A" tank to avoid mixing it with phosphate fertilizers, which can cause the precipitation of iron phosphates (Wieler and Sailus 1996), resulting in iron deficiency in the plants. If acids are used for pH correction, they are generally added to either

the "A" or "B" tank or can be added to a third stock tank a "C" tank. If potassium bicarbonate is required for pH correction, it should be added to a third tank, the "C" tank to avoid the risk of raising the pH in the other stock tanks which could result in the other fertilizers coming out of solution. The fertilizer feed program is designed to supply specific quantities of the nutrient elements to the plants per every unit volume of nutrient feed delivered to the plant. The absolute quantities of these nutrients is measured by the parts per million (ppm) targets. In addition to the absolute quantities of the nutrients in the feed, the relative ratios of one nutrient to another (particularly the N:P:K ratio) is also an important component of the feed program. Direct measurement of the various component nutrients contained in the feed solution, and the determination of the relative ratio of the nutrients comes from a lab analysis of the feed solution. It is useful to have the feed solution tested regularly in order to monitor the actual nutrient levels being delivered to the plants. Lab analysis of the feed solution takes time and it is also important to be able to monitor the feed on a ongoing basis throughout the day. Measuring the electrical conductivity (E.C.) of the feed solution is a very useful tool in the day-to-day management of the fertilizer feed solution. Measurement of the E.C. of the fertilizer feed solution delivered to the plants can be used as an indirect measure of the level of nutrients reaching the plants. The feed program contains the appropriate quantities of dissolved fertilizer salts required to meet the nutrient requirements of the plants, and this solution has a corresponding E.C. In fact, the corresponding E.C. of most feed solutions delivered to the plants, when based on a nitrogen target of 200 ppm, is about 2.5 mmhos. Of course the other nutrients are present in their relative amounts with respect to nitrogen. Once the feed solution has been mixed to meet the targets, measuring the E.C. of the 1-times strength solution can serve as the point of reference for delivering the nutrients to the plants. The day-to-day management of the delivery of feed to the crop can vary and is based on the salt level of the feed solution. The feed solution can be used as a management tool to direct the development of the crop towards a vegetative or generative direction. The basis for this is the higher the level of salts delivered to the root zone, the more stress that is placed on the plants. The more stress that the plant is under, the more emphasis the plant puts on producing fruit and the less emphasis on stems and leaves. There are limits to the salt stresses that can be placed on the plants while still maintaining optimum production, as a high sustained yield is obtained through a balance of leaves and fruit throughout the season. However, using the feed solution to help optimize plant balance is a management tool. On cloudy days, plants can make use of higher fertilizer levels, than on sunny days where the plant has greater demands for water. Raising the feed E.C. on a cloudy day will provide more nutrients to the plants, lowering the fertilizer E.C. on a sunny day will provide a greater relative proportion of water to the plants. The

saltier the fertilizer solution, the harder the plant has to work to extract the water from the root zone. Management of the daily application of fertilizer to the crop is based on varying the E.C. of the feed solution. The general rules for managing the feed E.C. and the total amount of nutrient solution volume delivered to the crop on a daily basis is presented in the next section.

Management of Irrigation and Fertilizer Feed - Application of fertilizer and water

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Water and fertilizer are delivered simultaneously to the crop via the nutrient solution, and the amounts of water and fertilizer delivered varies with the changing requirements of the plants. The plant's requirements change as they develop from seedlings to mature plants and in accordance with the day to day changes in the growing environment. In order to manage the delivery of nutrients and water to the plant, it is important to have a way of determining the crop's requirements for fertilizer and water.

Figure 18. Typical fertilizer feed system with two fertilizerstock tanks and computerized control of pH and E.C.

Feed monitoring stations are established throughout the crop, one or two stations per every 0.4 hectare (1 acre) of greenhouse area are usually sufficient, but having one monitoring station for every watering "zone" of the greenhouse is a good idea. The purpose of the monitoring station is to measure the volume of feed delivered to the individual plants, and to determine the volume of feed solution leachate, or "over-drain" that is flowing past the plants and out of the root zone over the course of the day. The E.C. and pH of the feed solution is taken on a daily basis, as is the E.C. and pH of the leachate.

Daily monitoring the percentage of feed solution volume flowing through

the root zone environment, the sawdust bags, or rockwool slabs etc., is used to adjust the volume of feed solution delivered to the plants. The E.C. of the leachate is used to make adjustments on the feed solution E.C. Monitoring the pH of the feed and leachate helps to ensure that the correct pH is being fed to the crop and gives an indication of what is happening in the root zone with respect to pH. Optimum feed pH is approximately 5.8, and this pH optimum also applies to the root environment as well. Generally the activity

of the roots tends to raise the pH in the root environment and feeding at a lower pH can help counteract this rise in pH.

Figure 19. General schematic of a fertilizer feed monitoring station. It is not recommended to feed at a pH of lower than 5.5 when attempting to lower the pH in the root zone. In addition to feeding at a pH of 5.5, the use of ammonium nitrate at 2 to 5 ppm of ammonium nitrogen (NH4 - N) will help to lower the pH of the root zone due to the acidifying effect of this fertilizer. A schematic of a typical feed monitoring station is presented in figure 19. In addition to monitoring the feed and leachate, recording the leachate percentage, feed and leachate E.C. and pH can be used as a tool to chart the performance of the crop with respect to these recorded values over time, and in relationship to other parameters including the amount and intensity of available light. The amount of nutrient solution delivered to the plant on a daily basis can be determined by the percentage over-drain or leachate that is recovered from the plants over the course of the day. Leaching, or allowing a certain percentage of nutrient solution applied to the crop, to pass through the root system, allows for a flushing of the root zone to avoid the accumulation of salts. Generally, when the plants are young, a percentage leachate of 5 to 10% is a good target. As the plants develop, the amount of water required to attain this over-drain target increases. As the season progresses and the light levels increase and the plants mature and begin to bear fruit, the over-drain targets increase to 20 to 30%. Generally these higher over-drain targets apply as the high light period of the year begins, usually in June. As the percentage over-drain decreases, the leachate E.C. increases, that is, the amount of salts in the root zone increases. The general rule for managing the level of salts in the root zone is that the root zone E.C. should not be greater than 1.0 mmho above the feed E.C. The design of the feed solution is based on delivering adequate nutrition to the plants, and these feed programs usually have an E.C. 2.5 mmhos (this is largely dependent on the E.C. of the irrigation water). With the optimum feed solution E.C. at approximately 2.5 - 3.0 mmhos, the salt levels in the root zone should be maintained at around 3.5 - 4.0 mmhos. Early in the crop cycle, the salt levels in the root zone can be maintained at the proper target fairly easily by increasing the volume of nutrient solution delivered to the plant to ensure a 5 to 10% over-drain. As the season progresses and the

water has been increased so that the upper limit of 30% over-drain has been reached, and the E.C. of the over-drain continues to climb above the target of 3.5 - 4.0 mmhos, the E.C. of the solution can be dropped. The reduction in feed solution E.C. is accomplished in stages with gradual, incremental reductions in feed E.C. in the order of 0.2 mmhos every 2 to 3 days. It is never advised to apply straight water to the plants in order to lower the root zone E.C., since the rapid reduction in root zone E.C. and increased pH can reduce the performance of the crop and compromise the health of the roots (Maree 1994). During periods when the plants are in a rapid stage of growth, the E.C. in the root zone can be below that of the feed solution. For example, the feed can be at 2.5 mmhos while the leachate E.C. may be a 2.0 mmhos. This is an indicator that the plants require more nutrients and the feed E.C. should be increased in increments in the order of 0.2 mmhos until the E.C. in the root zone begins to approach the upper target limit of 4.0 mmhos. By varying the volume and E.C. of nutrient solution delivered to the plants, in accordance to the leachate over-drain and E.C. targets, it is possible to optimize the delivery of adequate water and nutrients to the crop without over watering and over fertilizing. Applying too much or too little water can compromise the health and performance of the crop. The delivery of water to the plants occurs over the course of the entire day. Watering can be scheduled by using a time clock or in more sophisticated systems the watering events can be triggered by the amount of incoming light received by the greenhouse. In general, the greater the ability to control the delivery of water, the greater the ability to maximize crop performance. A starting point for watering the crop early in the crop cycle would be to apply water every half hour from one half hour after sunrise to approximately one hour before sunset. The amount of water required to meet the over-drain target is divided amongst the waterings based on the duration of the individual waterings. For example if a 40 second watering delivers 100 ml of water, then 10 watering events are required to deliver one litre of water. When more than a litre of water is required in one day the duration of the individual watering events can be increased, or the number of watering events can be increased or both. Generally, as the crop matures, it is better to increase the frequency of watering events than the duration of each event. If the watering system allows the variation of the frequency and duration of the watering events over the course of the day, then it is possible to increase the frequency and/or duration of the watering events during the high light period of the day without necessarily increasing the duration of the early morning or late afternoon watering events. Watering frequency can be used to help direct the vegetative/generative balance of the plant. For any given volume of water that is delivered to the plants, the more frequent the waterings throughout the day, the more the plant will be directed to grow vegetatively. The longer the duration between waterings, the stronger the generative signal sent to the plant. Frequent watering during the summer months in Alberta can help balance plants that

are overly generative due to the intense sunlight, high temperatures and low relative humidity. When the concept of percent over-drain is discussed, it is preferable to obtain the majority of the over-drain during the high light period of the day. The first of the over-drain should start to occur at 10:00 am and the greater part of the daily over-drain target should be reached by 2:00 to 3:00 p.m. Having the capability of varying the duration of the watering events over the course of the day allows for more nutrient feed being delivered to the plants between 10:00 am and 2:00 - 3:00 p.m. The use of over-drain targets is one way to ensure the plants are receiving adequate water throughout the day. Another strong indicator of whether or not the plants have received adequate water during the previous day is whether the growing points, or the tops of the plants have a light green color early in the morning. Over the course of the day when the plant is under transpiration stress, the color of the plants will progress from a light green to a darker blue-green. If the plants have received adequate water throughout the previous day, the light green color will return overnight as the plant recovers and improves its water status. If the plants remain a darker bluish-green in the early morning, the amount of water delivered the previous day was inadequate. Usually, this means that the over-drain target for the previous day have not been met and the amount of nutrient solution delivered to the plants has to be increased. During the summer months, under continuous periods of intense light, the plants may not have recovered their water status overnight even when the daily over-drain targets have been met. The plants begin the day a dark blue-green in color, an indication that they are already under water stress, even though the day has just begun. Under these circumstances the overdrain targets for the day could be increased, but there is the associated risk of over-watering and decreasing root health and performance. In these cases it is advisable to consider one or two night waterings, one at approximately 10:00 p.m. or one at 2:00 am or both. Usually the night watering events are the same length of time as the minimum watering duration applied during the day. Night watering can also help increase the rate of fruit development, but there is an associated risk of fruit splitting if too much water is applied at night. The night waterings should not be continued indefinitely and the decision to use night watering events and to continue with night watering has to be based on the assessed needs of the crop. The management of the feed solution, and its delivery to the crop has to be relatively flexible to meet the changing needs of the crop. With experience, growers gain more confidence and skill in meeting and anticipating the changing needs of the crop throughout the crop cycle and through periods of fluctuating light levels. The general information presented in this section serves as a starting point and by following the principles of over-drain management, E.C. and pH monitoring and correction, a successful strategy for delivery of water and nutrients can be established.

As with many things there is no one "right" way to apply water and nutrients to the crop. The use of leaching, although ensuring that salt levels do not accumulate to high levels in the root zone, does result in some "waste" of fertilizer solution as runoff. There are strategies that can be employed to minimize the waste associated with leaching. Collection and recirculation of the leachate, with an associated partial sterilization, or biofiltration of the nutrient solution is one approach (Portree 1996, Ng and van der Gulik 1999). The sterilization or biofiltration steps are required in order to minimize the disease risk associated with recycling nutrient solutions. Some estimates place the fertilizer cost savings at between 30 to 40% when recirculation is used (Portree 1996). In addition to being economical, recycling nutrient solutions is an environmentally sound practice (Zekki et al 1996). There is a limit to how long nutrient solutions can be recirculated, prolonged recycling of the same solution can negatively affect growth and yield. This is primarily associated with the accumulation of sulfate ions in the solution (Zekki et al 1996). In addition to sulfates, chlorides and bicarbonates also have a tendency to accumulate and can influence crop growth (Zekki et al 1996). The progressive accumulation of sulfates in recirculating solutions require occasional "refreshing" of the solution whereby the solution would have to be allowed to leave the greenhouse as waste (Zekki et al 1996).

Production of Sweet Bell Peppers

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Introduction

Greenhouse sweet bell peppers are a high impact superior product primarily grown in three colors; red, yellow and orange. The majority of commercial production area is based on red (85%), followed by yellow (10%) and orange (5%), however these percentages are subject to change to meet shifts in consumer demand. No matter what the final color of the pepper, all sweet

Figure 20. Ripening red sweet bell pepper.

peppers start out green in color and the final color develops as the fruit ripens. The color of the mature pepper is determined by the cultivar grown. Harvesting the fully sized peppers when they are still green is not profitable as the mature colored peppers command a better price.

Greenhouse pepper production is based on a full year cycle (Figure 22). The transplants go into the production greenhouse in approximately mid to late December at 6 weeks of age, the first pick of fruit begins in about late March, early April and continues to the following December. The greenhouses are empty for only 2 or 3 weeks during the year to allow for the removal of the old crop, the thorough cleaning of the greenhouse and to set up the greenhouse for the new crop. One crop a year is grown, that is, production for the entire year is based on the same set of plants. As it takes approximately 20 weeks (4 months), from seeding the crop, to first pick, as a result growing more than one crop a year is not considered profitable.

When the cropping cycle is considered, it is not recommended to carry a fully producing crop over the month of December. The reason for this is that the lower winter light levels do not support profitable crop production. This is also the reason why December is usually the month when crops are pulled and the new crop goes in. The use of supplementary lights are also generally not cost effective for trying to carry a producing crop over the winter months, through December, January and February. The prices received for the crop in the winter months are always higher than in summer when the greenhouse produce competes with the field produce. Winter production would offer considerable price advantage for produce if the yield and quality of the fruit were maintained. As crop production techniques improve, running a producing crop over the winter months may prove profitable, and staggered crop schedules and inter-cropping (planting young seedlings amongst an already producing crop) may allow for full year production. However, this manual will discuss pepper crop production following the single crop cycle outlined in Figure 22. An approximate target yield for introductory growers would be 23 kg/m².

Figure 21. Yellow sweet bell pepper.

Figure 22. Typical sweet bell pepper production cycle.

Figure 23. Orange sweet bell pepper.

Sweet bell peppers are grown as a tall crop, and provisions for working a tall crop must be incorporated into the greenhouse in order to grow the crop successfully. The main structural consideration for greenhouse sweet pepper production is the height of the greenhouse, the gutter height. A minimum recommended gutter height for sweet peppers would be 3.9 meters (13 feet), and the trend in greenhouses is to build them taller, with some greenhouses coming in at 5 meters (17 feet) at the gutters. The overhead support wires that support the weight of the plants, are generally .3 meters (1 ft) below the gutter, and this serves as an approximate limit to the crop height. Having high gutters essentially allows for a level of "forgiveness" in pepper production. If the plants become unbalanced during the production cycle, and put more resources into vegetative production, they can grow taller in a short period of time. With higher gutters growers are able to bring the plants back into balance without necessarily have to worry that the crop will reach the roof too early in the crop cycle, resulting in early termination of the crop.

Other considerations for working the pepper crop as it grows taller, are the provisions for being able to work with the plants, pruning and harvesting. The pipe and rail system allows for electric carts to run on pipe rails along the length of each of the rows of the crop. These carts have adjustable platforms that can be raised to allow employees to continue to work the crop as it grows taller. It is important that the carts be designed for maximum stability when tall crops are worked, and as gutter heights increase in new greenhouses, the width of the rails also have to increase to ensure the safety of those working on the carts.

Figure 24. Young sweet bell pepper developingtowards full size and eventual mature color.

CultivarsSelection of greenhouse sweet pepper cultivars is dependent on color, disease resistance, performance and yield. A variety of seed companies and distributors offer greenhouse sweet pepper cultivars, and the "latest" cultivars are always subject to change when superior cultivars are developed. Before selecting cultivars, investigate what is currently being grown by the industry in your area as the suitability of cultivars can vary depending on region (Portree 1996). It is also not recommended that more than one color of pepper be grown in the same greenhouse unless they are grown in separate environments. The cultural requirements of the different cultivars can be distinct enough to require that the environments be managed differently in order to obtain maximum yield.

Pepper Plant PropagationSeeding

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

The seedling nursery or propagation area should be cleaned and disinfested with a 10% bleach solution or other disinfesting compounds. Ensure that fresh seed is used, seed greater than one year old can have reduced germination and vigour. Seeding takes place approximately November 15, although the date can vary depending on the grower. Seed into rockwool plugs that have been wetted

with a feed solution with an E.C. of 0.5 mmhos at 25 to 26 °C. Use a standard pepper feed solution at approximately pH 5.8, and that has been diluted from an E.C. of 2.5 to 0.5 mmhos. Ensure that the temperature of the seeded rockwool plugs is maintained at 25 to 26 °C during germination, and maintain the relative humidity in the nursery at 75 to 80% ( VPD of 3 to 5 gm/cm³). Maintain air temperatures at 25 to 26 °C day and night. Do not allow the plugs to dry out, keep them moist using the warm (25 to 26 °C), 0.5 mmho pepper feed solution. The pepper seedlings should begin to emerge in about 7 to 10 days, use supplemental light to ensure approximately 140 to 160 W/m² , 18 hours a day (Portree 1996, Demers and Gosselin 1998). Once the seedlings have emerged, the temperature of the rockwool plugs should be reduced to 23 - 24 °C. The seedlings can be misted lightly once a day for the first four days after emergence. Four days after the seedlings have emerged, allow the relative humidity to drop to 65 to 70%. Do not allow the rockwool plugs to dry, apply light applications of the 0.5 mmho feed solution, the plugs should be moist but not sopping wet.

First transplanting: Into the rockwool blocks

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

At approximately 2 weeks after seeding, when the first true leaves are visible, the seedlings are transplanted into the larger rockwool cubes. The rockwool blocks are well wetted with full strength feed solution, E.C. 2.5 mmhos at approximately 23 °C, prior to transplanting. The seedling rockwool plug is rotated 90 degrees as the seedling is placed into the rockwool cube (Figure 25). This allows for more root development along the length of the young stem. The root-zone temperatures should be allowed to drop to 21 °C just after transplanting. The blocks should be watered from the bottom (E.C. = 2.5 mmhos, 21 °C) every second day, again ensuring that the blocks remain moist, but not sopping wet. Target root-zone temperatures of 21 °C for the next 2 weeks, when the root-zone temperature is dropped to 20 °C. Maintain air temperatures at 24 °C. during the day and 22 °C at night, for a 24 hour average temperature of 22 °C. Once the seedlings have established in the rockwool cubes, monitor the E.C. of the cube twice a week, the E.C. will rise and can reach levels of up to 7.0 mmhos without damaging the seedlings. At three weeks after seeding, 1 week after transplanting, the E.C. of the feed solution should be reduce from 2.5 mmhos to 2.0 mmhos, to target a root-zone E.C. of 3.0 - 3.5 mmhos in the block when the plants are ready for the second transplanting directly into the production greenhouse. As the plants establish and develop in the rockwool blocks, care must be taken to ensure that they have adequate space. Crowded plants will stretch, become tall and spindly, and result in poorer quality transplants. The plants should be spaced whenever their leaves begin to touch. Maintain supplementary lighting, 18 hour days at 160 W/m².

Figure 25. Transplanting the young seedlings into the rockwool blocks, the plug is rotated 90°as it is placed into the space in the top of the block to allow for more root development At five weeks after seeding the plants the target rootzone temperature should be 20 °C. The supplemental lighting is reduced from 18 hours to 14 hours in order to help reduce the "light shock" once the young plants are transplanted into the production greenhouse where no supplemental lighting is used (Portree 1996). The air temperatures should be 20 °C day and night (24-hour average of 20 °C ). The root-zone E.C. should now be in the range of 3.0 - 3.5 mmhos, never water with clear water in order to reduce rootzone E.C.

Figure 26. Monitoring to ensure that the proper temperaturesare maintained.

Growing media in the production greenhouse

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

There are a number of options for the type of growing media used in the production greenhouse, and these are outlined in section "Growing Media." The remainder of this focuses on sawdust as the growing media.

Planting Density

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Before the young plants are transplanted, the production greenhouse is set-up to receive the plants. A planting density of 3 plants/m² is recommended. The sawdust bags are laid down in double or single rows in accordance with the requirements to meet the planting density target. To determine the number of plants required for the greenhouse multiply the production area (in meters) by 3. The standard pepper sawdust bag will hold three plants, it has a volume of approximately 20 litres with dimensions of 23 x 86 x 10 cm (10 x 34 x 6 inches) when full. The number of rows required is then calculated. Using the example for double rows, the walkway, the distance between bags from adjacent double rows is approximately 76 centimeters (30 inches). The distance between bags in the two adjacent single rows of the double row is approximately 20 centimeters (8 inches), with a total width of 70 centimeters (28 inches)for the full double row. Using this information allows for the determination of number of double rows that can be placed in the greenhouse. In actual fact, determining the number and location of the rows occurs very

early in the greenhouse construction phase, as the drainage ditches and the pipe and rail heating system are "fixed" and put in-place well in advance of the crop.

Figure 27. Plants are spaced as soon as their leaves beginto touch, this prevents the plants from "stretching."

Knowing the number of bags required and dividing this number by the number of rows (double rows preferred), you will arrive at the number of bags required per row required to reach the target plant density. The number of bags in a row are spaced out evenly along the length of the row.

Transplanting into the production greenhouse; "house-set".

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

The young plants are ready to be transplanted into the production greenhouse at 6 weeks of age. The plants should be approximately 25 cm (10 inches) tall, have about 4 leaves on the main stem and will have begun to branch. The main stem usually branches into 2 to 3 branches, the point of branching is sometimes referred to as the "fork". Examination of the underside of the rockwool blocks should reveal a number of roots beginning to develop through the bottom of the block. This is another indication that the plants are ready to be transplanted onto into the greenhouse to allow the roots to "knit" into the growing media, e.g. sawdust bags or rockwool slabs.

Figure 28. Conditioning the sawdust bags 24 hours prior to "house-set."

Figure 29. "House-set'" transplanting into the production greenhouse.The growing media should be wetted, or "conditioned" with nutrient feed solution (E.C. 2.5 - 3.0 mmhos) for 24 hours before the plants are set onto the media. The general rule is to condition the media with feed solution at the same E.C. as exists in the rockwool block. It is also important to ensure that the media is at 20 °C, and that this root zone temperature is maintained throughout the remainder of the growing season. The plants are then set onto the media ensuring good contact between the bottom of the rockwool block and the growing media. If sawdust bags are used as the growing media, two to three plants are grown per 20 litre sawdust bag and the bags are slit to provide drainage. The slits are approximately 4 cm (1.5 inches) long, and are made on the sides of the bags facing the drainage channel, with one slit placed between each of two plants. The slits are made to allow for complete drainage of the bags and to avoid "pooling" of the feed solution at the bottom of the bag. For the first week in the greenhouse the day/night temperatures are maintained at a constant 20 - 21 °C, target a relative humidity of 70 to 80% ( VPD of 3 to 5 gm/cm³). Maintain CO2 levels at 800 to 1,000 ppm. The primary goal at this stage of the production cycle is to establish the young pepper plants on the media and ensure that they develop a strong root system. Generally speaking, if the plants do not establish strong roots early, when they are quite young, they will not develop a strong root system later in the season once the focus of the plants shifts towards fruit production. Careful attention should be paid to the application of the feed solution, target a 5% overdrain. Overwatering at this point will hinder the development of a strong root system, resulting in a root system that will not perform well under the intense light conditions in the coming summer months. Increase the amount of nutrient solution delivered to maintain the 5% overdrain target as the plants grow larger. Maintain a feed E.C. of 2.5 -

3.5 mmhos, the rootzone E.C. can be allowed to rise to about 4.0 to 4.5 mmhos, as the season progresses and light levels begin to improve, the rootzone E.C. should be brought down to 3.5 to 4.0 mmhos.

Figure 30. Young plants rooted well into the bag, twoweeks after transplanting.

One week after house-set target day temperatures of 21 °C and night temperatures of 16 - 17 °C for a 24-hour average of 20 - 21 °C. The optimum temperature for vegetative growth in peppers is between 21 and 23 °C and for yield about 21 °C (Bakker 1989). Establishing the difference in day/night temperature, while maintaining the target 24-hour average temperature, directs the plants to set flowers and maintain enough vegetative growth required for optimum fruit development and yield.

Pruning and plant training

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Pepper plants are indeterminate plants, that is, they continually grow new stems and leaves. For this reason the plants have to be pruned and trained on a regular basis in order to ensure a balanced growth for maximum fruit production. Pepper plants are managed with two main stems per plant, resulting in a density of 6 stems/m² from an initial planting density of 3 plants/m2. Pruning also improves air circulation around the plant which helps to reduce disease (Horbowicz and Stepowska 1995). Plants are generally pruned every two weeks. As new leaves and lateral side shoots develop from the axils of the new nodes on the growing stems, they have to be pruned to maintain the two main-stem architecture of the plant. The pepper flowers also develop at the nodes. A node is defined as a point on the stem from which leaves arise (Tootil and Blackmore 1984) and the length of stem between nodes is called an internode. The term "axil" refers to the upper angle formed by the junction of a leaf (or lateral) with the stem (Tootil and Blackmore 1984). After about 1 week in the greenhouse the all the plants will have developed 2 to 3 stem shoots at the fork. At this point the plants should be pruned to leave the two strongest stems. These two stems will be managed to carry the full production of the plants throughout the year. Each stem will grow to a height of up to 4 meters (13 feet) and require support in order to remain upright. Twine hung from the overhead support wires is used to support each

stem. The twine is tied to the main stem about 30 centimeters (12 inches) up from the block, one length of twine per stem. Ensure that the twine is not tied too tightly to the stem or the stem can be damaged as it expands. One other approach with the twine is to lay the twine on the sawdust bag just before transplanting the plant onto the sawdust. As the plant roots into the sawdust it secures the twine. Enough slack is left in the twine so that it can be twisted around the stem as it grows and develops throughout the year. Early in the season the plants are pruned to one leaf per node, that is the main leaf at the node is allowed to develop and the lateral stem developing from the node is removed. Beginning in April, a second leaf can be left to develop at every node on the main stem. The lateral stem is allowed to develop to its first node, at which point a leaf develops as well as another secondary lateral stem. The secondary lateral stem is pruned out, leaving the first leaf on the original lateral stem as well as the primary leaf on the main stem. The reason for leaving this second leaf is to increase the leaf area of the canopy to both make better use of the increasing light levels and to provide shade for the developing fruit. In May a third leaf (two leaves on the primary lateral) can be allowed to develop on plants that are in perimeter rows. These plants receive more light because of their position next to the walls and the additional leaves provide the required shading to the fruit as well as increased photosynthetic area. Care has to be taken when pruning to ensure that the main stem is not "blinded", that the growing point of the main stem is not pruned out. If this occurs the main stem will not develop any further. The main approach to avoid blinding the main stem is to allow the lateral to develop 1.5 to 2.0 centimeters (0.5 to 1.0 inches) before pinching it out. This allows the lateral to be clearly identified an makes it easier to be very clear on what is being removed to ensure that the main stem growing point is left intact. It is important to keep the pruning current with the development of the plant. Once pruning falls behind, there is really no catching up without sacrificing some yield, as too much of the plant's resources were allowed to go into undesirable leaf and stem production. Pruning is done using the fingers or small scissor cutters to ensure precise removal of the laterals and avoiding any damage to the main stem or main stem growing point. When pruning the plants use a powdered milk solution to dip hands between plants, the protein in the milk works to inactivate viruses that could potentially spread from plant to plant. The use of milk should continue until June (Portree 1996).

Flower and fruit set

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

The primary goal in managing the young pepper plants is to establish a strong vegetative plant on the bags. However, it is important to know when to target the first fruit set and start to establish the balance between stem and leaf production and fruit production. The presence of fruit will reduce vegetative growth (Bakker 1989) as the balance is established. Pruning and training of the leaves and stems then allows for matching the vegetative growth with fruit growth. Once this balance is established it is important to work to maintain the balance for continual, steady production throughout the season. If the crop goes 'out of balance' the production of fruit can occur in flushes interspersed with periods of vegetative growth where growers have to work hard to direct the plants back into a generative, fruit producing direction. Once the pepper crop establishes a pattern of production i.e. flushes of fruit production, it is difficult to direct it away from this pattern to a more steady cycle of fruit production. Flowering, fruit set and fruit size are related to the 24 hour mean temperature as well as to day/night temperature fluctuations (Bakker 1989, Khah and Passam 1992). Fruit set is increased by low temperatures but, fruit development may be affected by pollen infertility (Bakker 1989, Khah and Passam 1992). The day/night temperature difference can be used to direct the plant to set flowers and fruit, while the 24-hour average temperature can be used to ensure proper fruit development in the shortest time (Bakker 1989). The optimum temperature for flowering and fruit set in pepper is 16 °C (Pressman et al 1998), while the optimum 24-hour temperature for yield is about 21 °C. However, the day/night temperature difference is of minor importance compared with the effect of the 24-hour mean temperature for fruit set, fruit development and the fruit growth period of sweet pepper (Bakker 1989).

Pepper flowers are small under high night temperatures, where under low night temperatures they are large (Pressman et al 1998). The formation of malformed fruit is associated with problems with temperature during pollination. Flattened fruit or "buttons" indicate insufficient pollination as it is associated with the development of very few seeds per fruit (Pressman et al 1998). The functioning of female flower organs is inhibited at low night temperatures (14 °C or less) which gives rise to flattened fruit. The appearance of "button" pepper fruit in Alberta greenhouses is limited to early season fruit developed during the winter. This is the time of the year when providing precise heating to the "heads" of the plants would help improve flowering, fruit set, fruit development and fruit quality.

Pointed fruit which develop to a similar size as normal blocky fruit, are probably a result of an imbalance of pepper plant growth regulators (hormones) in the developing fruit

Figure 31. Flower and fruit set. (Pressman et al 1998).

At high temperatures, 32 to 38 °C, elongation of the style can occur with a resulting reduction on fruit set (Khah and Passam 1992). Fruit set is known to be reduced at temperatures above 27 °C and by low relative humidity (Khah and Passam 1992). There is also evidence of progressive reduction in fruit size associated with increasing light intensity during the high-light summer months (Khah and Passam 1992). Shading the greenhouse can offset some of the effects of high light intensity during a the summer months, using a 10% shading about the beginning of June.

The hot dry Alberta summers make it nearly impossible to maintain the optimum day-night, and 24-hour temperature targets without the use of some form of evaporative cooling (pad and fan or mist systems). However, the plants generally do not have trouble continuing to set flowers under these conditions. Stressful summer conditions direct the plants to remain generative and can push the plants to be too generative. The plants have to be managed to maintain adequate leaf cover and balanced fruit load, by leaving more leaves on the plants and targeting about 6 fruit per stem. If too many fruit per stem are allowed to set, and the plant is not directing adequate resources to leaf development, the plant will "stall" and will not be able to fill the fruit, resulting in yield loss. As the day/ night temperature difference is established one week after transplanting (while maintaining the 24-hour average temperature target of 20 - 21 °C), the plants will be directed to set flowers, with the first flower developing at the "fork'. The flower developing at the fork should be removed, with the first flower set and resulting fruit set targeted for the second node above the fork. After this flower sets, the flower at the third node is removed and the fourth node is left to develop. The flowers that follow at the fifth node and upwards are allowed to set freely. If the flower at the second node aborts, allow the third node to set a flower, if this flower sets, remove the flower at the fourth node and then allowing all subsequent flowers to set.

Figure 32. General scheme for targeting the first flower and fruit set. Maintaining the root zone temperature at 20 °C is also very important for the establishment of the plant balance. Lower root zone temperatures (approximately 15 °C) direct the plants to remain vegetative, and increases flower abortion and abortion of young fruit. Abortion of flowers and fruit is related to the rate of production of photosynthetic assimilates and the distribution of assimilate within the plant (Bakker 1989). The number of flowers and fruit creates a demand for plant resources, and if the plant cannot meet the demand due to low light levels etc. high rates of abortion of newly formed fruit can occur (Bakker 1989). The influence of low light levels resulting in flower abortion is thought to result if light levels are low between the fifth and tenth day following the visual appearance of the flower bud (Fierro et al 1994). Heating close to the developing fruit has been shown to enhance fruit development in tomato (De Koning 1996), and could prove beneficial for peppers. Practically, using an height adjustable heating pipe to maintain 20 °C near the top of the plant or "head" should improve flower set and fruit development during the cold winter months early in the season.

Unlike tomatoes, pollination of the pepper flowers occurs successfully without any outside pollination assistance required (assuming that the correct temperature targets are established). However, additional pollination assistance, bumble bees or "artificial" pollination has been demonstrated to improve flower set and eventual yield and quality of the pepper fruit (Portree 1996, Pressman et al 1998). However, it has also been shown that the beneficial effects of pollination appears related to the cultivar grown, with some, but not all cultivars demonstrating this enhanced development of fruit in response to pollination (Portree 1996). If bumblebees are used to aid pollination it is important to manage the

Figure 33. Young fruit, just set.bees to ensure that they do not visit the individual pepper flowers too aggressively which can result in scarring of the developing pepper fruit.

Irrigation

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Follow the general recommendations outlined in "Application of fertilizer and water." Target 5% overdrain early in the cycle and increase overdrain up 30% in summer. Increase the amount of water in accordance with the demands of the plant. If the plants have a light green 'halo' at the growing point in the morning, they received adequate water during the previous day. The root zone E.C. will rise if the volume of water is not adequate. Feed at an E.C. in the range of 2.5 to 3.0 mmhos to maintain a root zone E.C. of 3.5 to 4.0 mmhos. As the season progresses, and light levels improve, increase the number of watering events during the day to keep pace with the increasing day lengths. Night watering may be considered during the summer. Target the first watering within 0.5 hour of sunrise and the last watering about 1 - 1.5 hour of sunset. Target the first overdrain at about 10:00 a.m.. Pepper plants can take up to 3.5 to 4.0 litres of water a day during the summer.

Harvesting and Grading

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

It takes between 7 and 9 weeks from fruit set to harvest, taking longer during the low light periods of the year. The fruit is harvested at 85 - 90% color and a knife is used to make clean cuts on the peduncle (fruit stem) and care must be taken not to cut into adjacent fruit or stems.

Table 10: Guide to Pepper GradeSize

(Fruit diameter in millimeters)Grade

<80 mm Extra Large70 - 79 mm Large60 - 69 mm Medium50 - 59 mm Chopper

Fruit are graded according to size, and the larger sized pepper usually command a higher price. The size potential of pepper fruit is determined by the cultivar, but the management of the crop determines whether or not the maximum size potential is met for the greatest number of fruit picked. Fruit size, as with total crop yield, is a function of the management of the greenhouse environment and plant handling to establish and maintain the optimal plant balance.

Greenhouse Production Costs and Returns for Peppers***

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Total ($) $/Sq. FGreenhouse Production Area - 1999, Sq. Ft 58,560A. Gross Revenue 535,824 9.15Operating CostsGrowing Media, Seed/Cuttings 41,577.60 0.71Fertilizer & Chemicals 18,153.60 0.31Greenhouse Fuel 79,641.60 1.36Power & Water/Telephone 18,868.03 0.34Greenhouse Insurance 7,612.80 0.13Building & Machinery Repairs 6,441.60 0.11Auto Fuel, & Repairs/Insurance & Restr. 15,225.60 0.26Property & Business Taxes 1,171.2 0 0.02Accounting, Legal &Office supplies 3,513.60 0.06Membership, Donations & Subscriptions 5,270.40 0.09Travel, Advertising & Soil Testing 2,342.40 0.04Marketing Costs & Freight 40,406.40 0.69Interest on Operating Loan 1,756.80 0.03Hired Labour/Insurance &Benefits 116,534.40 1.99Miscellaneous costs 7,613.00 0.13 B. Total Operating Costs 336,128.83 6.27

Investment CostsOperator's Labour 38,064.00 0.65Interest Costs 60,902.00 1.04Depreciation 37,049.00 0.63C. Total Investment Costs 136,015.00 2.32

D. Total Production Costs (B+C) 502,144.00 8.58

Return Over Operating Costs (A-B) 169,695.00 2.90

Return to Management (A-D) 33,680.00 0.57Notes:

1. Most of the greenhouse operations are using "Biological Control" for pests

2. Miscellaneous costs include bank service charges, equipment lease/rental, crop supplies and construction material, etc.

3. Operator's labour is included under investment costs 4. Return to management is excess of revenue over all expenses

*** Nabi Chaudary, 1999

The Zen of Greenhouse Peppers

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Greenhouse peppers can be a challenging crop to grow. Once the plants establish a pattern of growth it can be difficult to manage them in another direction. For example, if the plants are strongly vegetative, it can take some time to direct the plants to be more generative, and vise versa. It is important to establish the proper balance in the plants as early as possible in order to set the stage for continuous, sustainable production and resulting high yields. Particular points of challenge with pepper production include setting and holding the first fruit. Fruit set is targeted at the second or third note above the fork where the plant breaks into two stems. The challenge here is that the young plant is generally strongly vegetative, a requirement for good establishment in the sawdust bag and eventual filling of fruit, and such plants tend to want to remain vegetative. By establishing the proper 24-hour average temperature of about 20 to 20.5 °C with a day temperature of 21 °C and a night temperature reaching 16 - 17 °C and holding this regime, the plants will be directed to set and hold fruit. The next point of challenge is to have an adequate fruit load established on the stems before the first fruit are picked. If the first fruit set, and subsequent flowers do not set, when the first fruit are harvested, all the energy of the plant goes towards vegetative growth. The plants will "race" to the wire with a resulting significant loss of yield. Once a good balance is established in the plants, maintaining about 5 to 6 developing fruit per stem (10 - 12 fruit/plant) at all times with fruit taking approximately 7 weeks to mature, then the crop will likely stay in balance to the end of the season. This assumes no drastic changes in the management of the crop of course. As the season progresses it is important to pay close attention to the plants, the following are a few signals that the plants may exhibit and an explanation for what the signals indicate.

Flowers

Flowers upward facing, weak. The plant is too generative, reduce night temperature to drop the 24 hour average temperature by 1 °C . This will direct the plant to be more vegetative. Weak

flowers usually occur during the summer months, although they can show up earlier if the greenhouse is run too warm.

Flowers large, bullish, thick peduncles, flowers opening downward. The plant is too vegetative. Raise the night temperature to bring the 24-hour average temperature up by 1 or 1.5 °C. The fruit from these large flowers often abort or are deformed.

Flowers opening downward, right-sized.

Normal flowers, the Zen state.

Fruit

Fruit abortion. Most fruit abortion occurs within 1 week of fruit set and is related t the "unwillingness" of the plant to carry the fruit. The plant is either too vegetative and needs to be directed to set and hold fruit by raising the 24-hour average temperature 1 °C, or is too generative and is dropping young fruit because it is already carrying too much of a load, Direct these plants vegetatively by lowering the 24 hour average temperature 1 or 2 °C. Misshapen fruit, tails. Most problems with fruit shape are related to poor temperature conditions during flowering. Usually seen when air temperatures fall below 14 °C for periods over the course of a few days., primarily during the winter months. Lygus bugs can also cause fruit shape problems, the bugs fed by inserting their mouthparts into the very young peppers, much like

mosquitoes feed on people. The damage becomes apparent when the fruit continues to develop and the damaged tissue tears open. Lygus bugs can even "top" he plant by killing the growing point. Cracking/split fruit. Fine cracks on the skin, russeting occurs when the relative humidity in the greenhouse rises above 85%. Fruit splitting can occur as a result of high root pressures when the night air temperatures are cool and root zone temperatures are high. It is also important not to water too late in the day. Sizing but not reaching mature color. Peppers reach mature size, but do not completely reach mature color over the entire fruit, even after 8 weeks. This condition is thought to be related with lower 24-hour average temperatures. Raising the 24-hour average temperature 0.5 °C should help to correct this problem in the crop. Premature fruit drop. A condition when fruit mature to size, and not yet to color, and premature abscission, or fruit drop occurs. The problem is seen early in the season affected the first fruit to size and appears to be related to low boron levels in the feed. Growers in sawdust are reminded that they may have to feed higher amounts of boron, 0.9 ppm, rather than the standard 0.5 ppm. Fruit reaching mature color but not sizing. Small fruit usually indicated a plant that is too generative, one that has put more resources into setting fruit and nor enough resources into developing the leaf area required to fill the fruit. These plants also have very short internodes, small leaves and appear stalled. Reduce the night temperature by 1 or 2 °C to direct the plant to be more vegetative. Target internode lengths of approximately 6 - 7 centimeters. Remember hat secondary fruit produced on laterals will always be smaller than primary fruit on the main stem. Blossom End Rot. This may appear at the blossom end or on the side of the fruit. Blossom end rot is due to a calcium deficiency, or reduced translocation of calcium to the fruit. It can result under conditions of lower transpiration or a shortage of water. A high E.C. in the root zone restricts the uptake of water. Maintain an active environment so that the plants are transpiring. If the problem does not rectify, apply a spray of 400 ppm calcium chloride solution to the plants. Sun scald. During the summer months under high solar radiation any fruit exposed to direct sunlight can develop sun scald. The symptoms of sun scald appear similar to those due to blossom end rot. Ensure that adequate leaf cover is maintained to shade the fruit from direct sunlight.

Leaves

Turning over, underside of leaves face up. This behavior is common when the plants are first set out into the production greenhouse and is also seen on established plants, usually in outside rows. The condition appears to be related to high vapour pressure deficits as when transplant are moved from the nursery into conditions of lower relative humidity in the greenhouse.

Curling, from the edges in. Seen primarily on older leaves, although some cultivars may have more of a tendency to exhibit this characteristic, this is not considered to be a problem. If excessive curling and twisting is seen on the young growth this can be an indication that herbicides have drifted into the greenhouse. Interveinal chlorosis. As the leaf ages, over 3 months old, the tendency of developing interveinal chlorosis increases. A result of ageing and senescence s these leaves are no longer as active in the development of the plant and fruit. The plant can "mine" the leaf, removing mobile nutrients for use on other parts of the plant. This behavior is normal. Interveinal chlorosis on the younger leaves can indicate a problem with the nutrient solution or that the root zone temperatures are exceeding 23 °C. It is important to keep the root zone temperatures in the 19 - 22 °C range. Large leaves. Large leaves are a sign of a strong vegetative plant. Not a problem if the fruit set is also good. Small leaves. Indicates that the plant is generative , which should also be apparent by a heavy fruit set. The plant may be too generative if the fruit is taking too long to ripen and are undersized. As well as lowering the 24-hour average temperature, under summer conditions it is recommended to have about 20 ppm of ammonium nitrogen. This will help to direct the plant to be more vegetative

End of Season Cleanup

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

The end of season cleanup is necessary to help ensure the success of next year's crop. A thorough cleanup is an important component of the pest and disease management program as it can prevent or minimize the carry over of pest and disease problems into the next season. All crop residue is removed from the greenhouse and disposed of. Depending on the area, facilities may exist to accept the crop residue for composting. The spent sawdust from the grow-bags could also be a welcome addition to compost sites as much decomposition of the sawdust has already occurred during the growing season. Once the crop has been removed, increasing the greenhouse temperature to over 25 °C for several days can increase the metabolic activity of any pests still in the greenhouse and can help cause them to die of starvation in the absence of their food source (Portree 1996). The interior of the greenhouse should be washed with a detergent solution using a pressure washer and then rinsed. The detergent will remove oily residues from the greenhouse and covering material. Following the rinse a 10% bleach solution can be applied to aid in disinfecting the greenhouse structure of any remaining pests and disease organisms. It is not recommended to apply detergent and bleach in the same operation in order to avoid chemical reaction between the bleach and the detergent. When pressure washing the greenhouse ensure that all safety precautions are taken to prevent direct exposure to the bleach solution. All greenhouse equipment should also be washed and disinfected. Dripper stakes, clips and truss supports (tomato greenhouses) should be soaked overnight in a 10% bleach solution and then rinsed. The irrigation lines should be flushed with nitric or phosphoric acid at a pH of 1.6 to 1.7 (1 part acid to 50 parts water) (Portree 1996). Do not allow the acid solution to contact the pH electrode sensors or the E.C. sensors as they can be damaged (Portree 1996). The acid solution should be allowed to sit in the lines for 24 hours at which time the lines should be thoroughly rinsed with water to ensure that all the acid solution is removed from the lines. CAUTION: Provide good ventilation through the greenhouse when flushing the lines with acid to avoid the build-up of fumes. Ensure that the flushed water does not have a pH of below 5 as dangerous chlorine gas may form (Portree 1996).

Steam Sterilization of Rockwool Slabs

If rockwool slabs are used instead of sawdust bags as the growing media, the rockwool slabs can be used again for the upcoming crop. The reuse of rockwool slabs is both environmentally

friendly and makes economic sense (Portree 1996). Good quality slabs can be used for up to three years (Portree 1996). Do not use slabs that have lost more than 10% of their original height (Portree 1996), as this is an indication that the structure or "profile" of the slab has changed such that the yield of subsequent plants grown can be reduced significantly. Steam sterilization can ensure that disease organisms do not carry over into the next season. Slabs should be as dry as possible as dry slabs heat faster than wet slabs (Portree 1996). If the crop has had tomato mosaic virus (TMV) or pepper mild mottle virus (PMMV) the slabs should be heated to 100 °C and held at this temperature for 10 minutes (Portree 1996), otherwise the slabs should be heated to 75 °C for 20 minutes (Portree 1996). If the slabs are bagged and palette, they require 5 hours to reach 100 °C (Portree 1996).

Pest and Disease Management

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Successful crop production requires that crop pests and diseases be managed so that the effects of diseases and pests on the plants are minimized. The management of crop diseases is directed at preventing the establishment of diseases and minimizing the development and spread of any diseases that become established in the crop. Managing pest problems is directed at preventing the pest populations from becoming too large and uncontrollable (Portree 1996). The presence of pests and diseases are a fact of crop production and growers must use all available options and strategies to avoid serious pest and disease problems. Integrated pest management (IPM) is a term used to describe an evolving process where cultural, biological, and chemical controls are included in a holistic approach of pest and disease control (Howard et al 1994). Key components of effective pest and disease control programs include: crop monitoring, cultural control, resistant cultivars, biological control and chemical control (Howard et al 1994, Portree 1996).

Crop Monitoring

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Crop monitoring is the continually on-going surveillance to detect the presence of a pest or disease at the very early stages of development of the disease or pest population, before economic damage has occurred (Howard et al 1994). Everyone involved in working the crop should be made aware of the common pest and disease problems and what to look for to detect the presence of problems in the crop. In addition this general surveillance of the crop, dedicated monitoring of the crop should be included in the weekly work schedule (Howard et al 1994, Portree 1996). Blue sticky cards, placed throughout the crop, are a useful monitoring tool to help trap and detect pest problems before they become a problem (Howard et al 1994). Yellow sticky cards are known to attract and catch some biological control agents e.g. Aphidius sp. (Don Elliott, pers comm) Biological control agents can be released well in advance of any pest population explosion thus allowing for the establishment of the control agents and prevention of a serious pest problem. Crop monitoring should begin when the crop is still on the seedling table or at the transplant stage (especially when transplants are obtained by another greenhouse ie. purchased from a propagator) (Portree 1996). If transplants are being purchased from a propagator it is important to be in contact with the propagator regarding any pest problems encountered during the production of the transplants. It is also important to know what pest control measures were used, if any, to control the problems. It is advisable to

establish in advance, what control measures you are willing to have applied to the transplants at the propagator's prior to receiving them into the greenhouse. The concern is that any pesticides that are applied are compatible with the pest control programs i.e. biological control programs that will be used for the duration of the crop. Some growers may insist that only biological controls be used during the production of transplants, and/or that biological control agents be introduced preventively to the transplants before they are received.

Cultural Control

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Cultural control involves providing the conditions that favour the growth, development and health of the crop, and where ever possible, providing conditions that work against pest and disease (Howard 1994, Portree 1996). Many disease causing fungi and bacteria require the presence of free water or condensation on the plants in order to cause disease (Jarvis 1992, Howard 1994, Portree 1996). High relative humidity promotes the development of disease, and maintaining the environment below 85% relative humidity will help to escape or avoid disease problems (Jarvis 1992, Howard 1994, Portree 1996). Ensuring proper ventilation and air movement within the crop canopy, as well as maintaining optimum plant spacing and a relatively open canopy, will ensure good air circulation and minimize the establishment of micro-climates that favour disease development. Proper contouring of the greenhouse floor will avoid the pooling of water which contributes to localized high relative humidity. Optimizing the greenhouse environment to favour the development of the plant will ensure a strong, healthy plant which is not only a prerequisite for high yields but also results in plants that are better able to resist diseases and insect pests (Jarvis 1992, Howard 1994, Portree 1996). Good crop sanitation is another important component of successful cultural control. The plants must be pruned and maintained on schedule, all crop debris should be promptly removed from the vicinity of the greenhouse. Any weeds that happen to gain a foot hold through gaps in the floor plastic should be removed immediately upon discovery and the floor repaired. Personal plants "pet" plants should not be grown in the greenhouse. Both weeds and "pet" plants can be as source and "haven" for pest and disease problems. Pruning tools and other equipment should be cleaned and disinfected on a regular basis. Aprons or other clothing worn by the workers should be washed frequently. When a disease or pest problem area exists in the greenhouse, that area of the greenhouse should be worked last, to avoid the spread of the disease or pests by the workers. In this situation, special care must be taken to disinfect tools and to clean clothing. Maintain a 6 to 10 meter wide buffer zone (Howard et al 1994, Portree 1996) around the outside of the greenhouse by regularly mowing any weeds that try to grow in this zone. The presence of plants in close proximity to the greenhouse can serve as a reservoirs for continual introduction of pests and

diseases into the greenhouse. Screening of the intake vents can also play an important role in excluding pests from the greenhouse. It is not enough just to screen-off the intake vents as the screening restricts the air flow into the greenhouse, it is important to ensure that the surface area of the screening used is large enough so that it does not restrict the flow of air into the intake vents (Chang 1996). This may require that a screen 'chamber' be constructed over the vent.

Resistant Cultivars

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Plant breeders have had considerable success in developing cultivars that contain genetic resistance or tolerance to diseases. When selecting the cultivars to be grown, it is important to consider the genetic resistance of the cultivars to the prevalent disease problems in the region (Howard et al 1994). The development of cultivars possessing genetic resistance to pests has been relatively unsuccessful (Howard et al 1994), however, the techniques of genetic engineering have made inroads in conferring pest resistance in plants. Genetically modified, pest resistant plants may become available to greenhouse growers in future. The development use of genetically modified plants or genetically modified organisms (GMOs) is currently a contentious issue, and may not be accepted by growers or consumers. Biological Control

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Biological control uses beneficial organisms, primarily predators and parasites, to control pest populations below economically important levels. The goal is to establish a balance between the pest population and its parasites and predators to keep the pest population under control. The complete eradication of the pest population is not the goal of biological control programs, as some pest organisms are required so the parasites and predators can reproduce. The greenhouse industry has a well established reputation for using biological pest control agents more than any other crop production industry. The reason for this is, in part, due to the ability of greenhouse growers to manage the environment to favour the biological control agents. Another factor is the relatively limited number of pest species in greenhouses, as well as a general tolerance of greenhouse crops to leaf damage caused by these pests. The high value of greenhouse produce is another reason why the use of biological controls is economical in greenhouse crops. The increased use of biological controls has led to a reduction in pesticide applications as the industry leads in environmentally responsible, intensive crop production. Effective biological control of diseases is a more difficult goal and to-date, has rarely been achieved (Howard et al 1994). However, research in developing biological controls for greenhouse crop diseases is ongoing and it is likely that biological control products for greenhouse diseases will be available in Canada in the near future. The primary strategy of biological control for greenhouse plant diseases is to introduce fungal parasites to control populations of disease causing fungi in the greenhouse environment so that they are unable, or have a reduced ability to infect the plants. Some of the promising biological control agents, for example, fungi in the Genus Trichoderma are also strong competitors of the disease causing fungi such as Botrytis cinerea, and can be used to protect wound sites to prevent Botrytis from colonizing the wound site.

Chemical Control

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Pesticides are valuable tools when used as a component of an integrated pest management program (Howard et al 1994). Insecticides should be applied only in support of biological control programs, dealing with localized pest outbreaks in the crop that have escaped the biological control agents. When insecticides are used, care must be taken to ensure that they are compatible with biological control agents, that there will be minimal long term adverse residual effects on biological control programs. Fungicides are used only when a disease problem is detected. Pesticides are regarded as the controls of last resort because their misuses creates high-profile environmental and food safety problems (Howard et al 1994). Also, the application of some pesticides to a crop can cause stresses that reduce the productive life of the crop and can make the plants

susceptible to other pests and diseases (Howard et al 1994). If the use of biological control agents is to obtain a balance between pests and predators that does not threaten the productive yield of the crop, the indiscriminate use of pesticides creates imbalance and uncertainty in the crop. A list of pesticides registered for use on greenhouse peppers in Canada is included in Appendix I.

Pests of Greenhouse Sweet Peppers and Their Biological Control

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Descriptions of the common pests of greenhouse peppers are followed with a list of the biocontrol agents recommended for control. Pesticides are not discussed. Pesticide recommendations can be obtained from a greenhouse crop production specialist.

Assessment of the Quality of Biological Control Agents

Biological control agents are living organisms and their ability to establish and control pest populations depends on their fitness. When ordering biological control agents ask the supplier what to look for to help assess the quality of the agents when they arrive. A hand lens or magnifying glass is very useful when inspecting packages of biological control agents. All packages of biological control agents should be inspected on arrival. Packages arriving during the winter should be checked immediately to ensure that they have not been frozen or subjected to cold temperatures. The inside of the shipping cooler should not be cold, if the ice pack contained within the cooler is frozen solid, it is likely that the entire package froze and the biological controls have been damaged or killed (Portree 1996). Packages received during the summer months should be cool inside, if they are hot then the biological control agents may be damaged or killed. Always release the biological control agents into the greenhouse as soon as possible after they are received. Follow the instructions provided with the package.

Aphids

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

The green peach aphid (Myzus persicae) is the most common aphid pest of greenhouse sweet peppers but there are other aphid species that can become a problem in greenhouse peppers. These other aphid species include; the melon aphid (Aphis gossypii), the potato aphid (Macrosiphum euphorbiae) and the foxglove aphid (Aulacorthum solani). Not all aphid biological control agents are equally effective on all aphid species so it is necessary to be sure of the identity of the aphid species in question. All of the species eventually develop winged forms.

Green peach aphids are usually light green in color, but can be pinkish or yellowish in color in the fall (Howard et al 1994, Portree 1996). The body is about 1.2 to 2.5 millimeters long and egg shaped. The winged forms can have black or brown colored heads and black markings on the body.

The melon aphid adults are usually either black or green when there are just a few aphids present, but as the population grows and the aphids become crowded the colors can range from olive green to yellowish green. Melon aphids are about the same size as green peach aphids, 1 to 3 millimeters long, they can be distinguished from the other aphid species by the dark black cornicles and short antennae (Howard et al 1994, Portree 1996).

Figure 34. Green peach aphids.

Potato aphids are quite large, 1.7 to 3.6 millimeters long and the body is wedge-shaped and yellowish green to pink in color (Howard et al 1994). The head has prominent antennal tubercles that are directed outwards (Howard et al 1994). Potato aphids will drop off the leaves when disturbed (Howard et al 1994).

Figure 35. Key to the wingless forms ofthe common aphids found in greenhouse peppers.

Foxglove aphids are smaller than potato aphids but larger than melon and green peach aphids. This aphid is a shiny light yellowish green to dark green in color with a pear-shaped body Howard et al 1994). The only markings on the bodies of wingless adults are darkish patches at the base of the cornicles (Howard et al 1994).

Aphids can be present in the pepper crop very early, even while the plants are just in the seedling stage. They can come in on the transplants as well. Aphids feed by sucking the plant sap. Symptoms of aphid infestation include the development of sticky honeydew on the leaves and fruit. The presence of honeydew on the fruit requires that the fruit be washed prior to going to market. Sooty mold is often associated with the aphid honeydew, this mold uses the honeydew as a food source and grows to resemble a layer of "soot" on the leaves and fruit. The presence of sooty mold on the fruit also makes washing the fruit a necessity. The growing points, young leaves, flowers and young leaves can be damaged and distorted. and in severe infestations flower abortion can occur.

Aphid control should be started in propagation with the introduction of parasitic wasps; Aphidius matricariae for green peach aphid, Aphidius colemani for the melon aphid and green peach aphid and Aphidius ervi for potato aphid. Another parasitic wasp Aphelinus abdominalis is effective against the potato and foxglove aphid. Parasitized aphids become silvery-brown in color with a small exit hole at the back when the parasite has emerged. The larvae of the midge Aphidoletes aphidimyza feed on most aphid species, but will

not feed on gall forming aphids (Don Elliott, pers comm) Aphid hot spots and population explosions may require introductions of lady beetle species, Harmonia axyridis, the Asian lady beetle and large scale introductions of Hippodamia convergens.

Introductions of these predators and parasites may have to continue throughout the entire season. For best results always use a combination of aphid predators and parasites. Consult your local supplier for information and recommendations on release rates.

Figure 36. White spots on pepper fruit caused by aphidfeeding on the fruit bud when it was still young.

Figure 37. A lady beetle adult consuming an aphid.

Figure 38. Aphidoletes midge larvae feeding on aphids.

Two-Spotted Spider Mite

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

The two-spotted spider mite (Tetranychus urticae) is a common pest of a number of greenhouse crops (Howard et al 1994, Portree 1996). Typical symptoms of two-spotted spider mite infestations include speckling of leaves and fine webbing on the underside of affected leaves. As the spider mite population increases, the leaves become brittle and brown in color, the amount of webbing on the leaves becomes very prominent and the mites can be seen milling about on the webs. It is very easy for the two-spotted spider mites to be "picked-up" on clothing and transported throughout the crop by workers. As the season progresses into fall, female two-spotted spider mites develop a bright orange-reddish color as they prepare for the winter. The female mites seek shelter in crevices throughout the greenhouse and a thorough end of season pressure wash clean-up is necessary to minimize the number of females that survive to the next crop.

Figure 39. Two-spotted spider mite.

Effective biological control of the two-spotted spider mite is obtained by introducing the predatory mite Phytoseiulus persimilis as soon as two-spotted spider mites are detected in the crop. P. persimilis does well in the pepper canopy, and once established throughout the greenhouse it controls the spider mite population for the remainder of the season. The mites Amblyseius fallacis and Amblyseius callifornicus are closely related to P. persimilis and establish well and gives better control under low density mite situations, but should be used along with P. persimilis (Don Elliot, pers comm).

Thrips

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Figure 40. Thrips.

There are two species of thrips that are common pests in greenhouse vegetable crops, the western flower thrips (Franliniella occindentalis), and the onion thrips (Thrips tabaci) (Howard et al 1994, Portree 1996). Thrips feed by opening wounds on the plant surface and sucking out the contents of the plant cells, the feeding results in small whitish streaks on the leaves and fruit and can cause distortions in the young developing fruit (Howard et al 1994, Portree 1996).

The adult thrips congregate in the flowers and regular monitoring of the flowers will allow for the early detection of thrips. Yellow and/or blue sticky traps placed throughout the crop, as with the other insect pests, will help in the early detection of thrips infestations. Avoid using yellow traps if Apidius sp. are being used for the control of aphids in the crop.

In addition to causing direct feeding damage and resultant yield loss, both thrips species are vectors

of Tomato Spotted Wilt Virus (TSWV) which can be a serious disease problem in peppers and tomatoes (Howard et al 1994, Portree 1996). One of the main control measures for minimizing the spread and infection of TSWV within the crop is to control the thrips vectors. There are a number of predators available for biological control of thrips: predatory mites Amblyseius degenerans, Amblyseius cucumeris, Hypoaspis miles and Hypoaspis aculeifer and predatory bugs, Orius insidiosis and other Orius species.

Loopers and Caterpillars

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

At least two species of loopers have been associated with problems in greenhouse pepper crops, the cabbage looper, Trichoplusia ni, is the most common, with the alfalfa looper Autographa californica being an occasional problem. The damage is caused by the larval stages which can reach 2.5 to 3.5 centimeters in length depending on the species. The cabbage looper is the larger the two species in the final larval stage. The larva are a light green in color with whitish stripes along the length of their bodies. The larvae feed on foliage and fruit, fruit damage consists of holes in the fruit, accompanied by frass on and around the calyx. As the loopers reach their mature size, the amount of feeding damage can be considerable.

Loopers generally enter the greenhouse through vents and other openings as adult moths which then lay eggs on the plants. The eggs hatch and the larval or looper stages begin feeding and complete their life cycle in about 20 days. As a result, a number of generations can be completed in the crop if control measures are not taken. Loopers overwinter as pupae, and can overwinter inside the greenhouse Figure 41. Looper on a pepper fruit.(Portree 1996). When the greenhouse enters the new production cycle, the moths emerge, mate and begin egg-laying in the new crop (Portree 1996). Screening intake vents will help prevent adult moths from entering the greenhouse. Pheromone traps can be used to detect the presence of adult moths in and around the greenhouse, and acts as an indicator for when to introduce biocontrol agents. Ultra-violet light traps are also used to catch adult moths. The egg parasite Trichogramma brassicae should be released as soon as adults are detected. The parasite Cotesia magriniventris should also be introduced, this parasite prefers to attack young loopers. Bacillus thuringiensis (B.T.) can also be used as part of the biocontrol program. B.T. is a microbial biocontrol agent which is activated once the loopers consume plant material which has been sprayed with B.T. Also, since the loopers are quite large, they can be removed by hand when they are found in the crop.

Figure 42. Looper feeding damage on a pepper fruit.

Figure 43. Looper feeding injury on pepper leaves.

Whitefly

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

The greenhouse whitefly (Trialeurodes vaporariorum) is a common and serious pest in greenhouse crops in Canada (Howard et al 1994). However, it is rarely a problem on greenhouse sweet pepper (Howard et al 1994). A second whitefly species, the sweet potato whitefly, Bemesia tabaci, has been found in some greenhouses in British Columbia (Portree 1996). Of the two whitefly species, the sweet potato whitefly is more difficult to control (Portree 1996).

Greenhouse whitefly adults are about two millimeters long and congregate on the undersides of the leaves. The usually fly short distances when disturbed. The whitefly nymphs are clear, flattened scales about 1.0 millimeter long at their largest size, and are also found on the underside of the leaves. The sweet potato whitefly is smaller than the greenhouse whitefly and is more yellowish in color (Portree 1996).

Figure 44. Greenhouse whitefly.

Whitefly damage the plant by sucking sap from the leaves. Large infestations can cause leaf yellowing and a general decline in the plant. Sooty mold is commonly found in association with whitefly. As with aphids, whitefly feeding also results in honeydew formation which can reduce fruit quality. The presence of the honeydew and sooty mold can necessitate that the fruit be washed prior to going to market. The presence of sooty mold on the leaves

can reduce the productivity of the leaf by reducing the amount of light reaching the leaf surface (Howard et al 1994). The parasitic wasps, Encarsia formosa and Eretmocerus eremicus, are effective against whitefly with parasitized whitefly scale becoming yellow or black in color, depending on the parasite. Scale parasitized by Encarsia formosa is black in color. Delphastus pusillus is a small beetle that feeds on whitefly eggs and is ideal for complementing Encarsia and Eretmocerus (Portree 1996).

Fungus Gnats

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Fungus gnats are commonly found in practically all greenhouse crops (Howard et al 1994). Fungus gnats are an indicator of moist conditions in the greenhouse and populations generally grow to be quite large early in the year or whenever there is pooling of water on the greenhouse floor. Adult fungus gnats range from 2 to 3 millimeters in length, while the larvae are 4 to 5 millimeters long. The larvae of the fungus gnats are the damaging stage and feed on the roots. They are generally not a problem in greenhouse tomato and pepper, but can be a serious in cucumbers (Howard et al 1994), especially young plants. Affected plants develop slowly and may eventually collapse if too much of the root system has been damaged (Portree 1996). There

Figure 45. Fungus gnats.

is evidence that fungus gnat adults may transport root rot fungi such as Pythium sp. and Fusarium sp. from plant to plant, contributing to the spread of disease caused by these fungi (Howard et al 1994). Fungus gnats are often confused with shore flies, as both are common in the greenhouse under wet conditions. Shore flies are slightly larger than fungus gnats, and look like scaled-down versions of house flies, while fungus gnats look more like tiny mosquitos that don't bite. Biological control of fungus gnats is obtained through the use of predatory mites Hypoaspis miles and most recently Hypoaspis aculeifer. Both of these predatory mites also have activity against thrips larvae that move to the base of the plants to pupate. Nematode parasites in the genus Steinernema are applied as a drench to the root zone and kill the fungus gnat larvae by penetrating the larvae and consume them from the inside.

Lygus bugs

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Figure 45. Fungus gnats.

Lygus bugs (Lygus spp.) are common pests of field crops in Alberta, particularly alfalfa and canola, and have become increasingly important in greenhouse vegetable crops (Howard et al 1994, Portree 1996). There are a number of species within the genus which can become pests in the greenhouse including Lygus lineolaris. When nearby alfalfa or canola fields are cut or harvested, large numbers of Lygus bugs can be displaced and move into the greenhouse. Lygus bugs can enter the greenhouse through unscreened vents.

Adult Lygus bugs can reach 5 to 6 mm in length and can range in color from green to brown with mottled black markings. Once in the greenhouse, Lygus bugs can continue their life cycle and establish a population within the greenhouse. Both the adults and nymphs feed on plant juices through piercing and sucking mouthparts. The bugs like to feed on the plants at the growing points and can damage the developing flower bud that in-turn results in malformed fruit.

Lygus bugs are relatively large, fast-moving insects which can be difficult to control with biologicals. Orius and Deraeocoris will feed on Lygus bugs (Portree 1996). Preventing the entry of Lygus bugs into the greenhouse by screening the vents offers the best prospect for controlling this pest.

Figure 47. Malformed fruit caused by lygus bug feedinginjury when the fruit was in the very young "bud" stage.

Earwigs

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

The European earwig (Forficula auricularia) can be quite common in greenhouses. These insects are brown in color and about 10 - 15 millimeters long. They are easily identified by the presence of distinctive "cerci", or appendages located at the back end of the insect. In the male earwigs, the cerci resemble pincers, the cerci are almost straight on female earwigs. Earwigs are often found under the sawdust bags or rockwool slabs or hiding in other dark, moist, protected areas. Earwigs are nocturnal and feed on a variety of things, including plants and other insects.

Earwigs have occasionally become a problem in greenhouse sweet pepper crops by moving into the crop canopy and damaging pepper fruit located up to one meter off the floor. The earwigs burrow into the fruit at the calyx, the damage resembling that caused by loopers. Cutting the fruit open often reveals a mature earwig. The holes in the fruit and the associated frass renders the fruit unfit for market.

Figure 48. Earwig.

Control of these insects is obtained by trapping them when they are still on the greenhouse floor, before they move into the canopy. Commercial traps and baits are available.

Diseases of Sweet Pepper - Fungal DiseasesDamping-off

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Damping-off is a disease of seedlings and occurs on the seeding table when the young plants are just beginning to grow. The disease is caused by a number of species of Pythium as well as Rhizoctonia solani. If the disease attacks the young plants as they are just emerging from the seed, the symptoms of this pre-emergent damping-off is simply seen as areas where no seedlings have emerged. Damping-off in young, emerged, seedlings is seen as a toppling over of the seedlings as the root systems are destroyed by the fungi. It is possible for some plants to be affected by these fungi and still develop into mature plants. If these plants are stressed later in the season the fungi can begin to progress in the plants causing a root rot which can eventually kill the mature plant. Damping-off is not common when seedlings are grown in inert media such as rockwool, it is more common in soil-based media. The disease is more common where greenhouse sanitation practices are poor (Howard et al 1994) or where growing conditions i.e. soil temperature, watering etc. are not optimal, and the young plants are stressed. As commercial greenhouse vegetable seedlings and transplants are grown in rockwool, under optimal conditions with proper plant spacing, this disease is generally of minor importance. However, if the young plants are exposed to stress conditions, particularly conditions of cold, excessively moist root zones, then the disease can occur. The best control for this disease is prevention, obtained by using high quality, fresh seed, and by maintaining optimal growing conditions for the young plants.

Pythium Crown and Root Rot

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Pythium crown and root rot caused by a number of Pythium spp. is not common in greenhouse peppers, however it can occur as an extension of an early damping-off problem in the seedlings or as a result of stressful conditions in the greenhouse at transplanting. Transplants infected by Pythium spp. develop slowly, are slow to root into and establish on the sawdust bags, and in extreme circumstances, wilt and slowly die.

The early stage of the crop cycle often determine the success of the entire year as it is important to go into the production cycle with strong, well established plants. The best method for the control of Pythium root rot is to ensure that optimal growing conditions, particularly root zone temperatures and watering, are maintained.

Fusarium Stem and Fruit Rot

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

The appearance of soft, dark brown or black lesions on the stems at nodes or wound sites are symptoms of Fusarium stem and fruit rot caused by Fusarium solani (Howard et al 1994). Black water-soaked lesions may also develop around the calyx, eventually spreading down the sides of the fruit (Howard et al 1994). Under conditions of high humidity the fungal mycelium is quite apparent on the lesions (Howard et al 1994). Maintaining a clean greenhouse and good sanitation practices are key factors in preventing fusarium stem and fruit rot. Infected plants should be carefully removed from the greenhouse and buried in a landfill. Maintain good air circulation and avoid conditions where the relative humidity rises above 85%. Avoid wounding fruit and excessive wounding to the stems.

Gray Mold

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Gray mold, caused by the fungus Botrytis cinerea, is a common disease of greenhouse crops grown under conditions of high humidity and poor air circulation. The fungus enters the plant from wound sites and olive-green lesions develop that can eventually girdle the stem causing the plant to die (Howard et al 1994). Fruit infections commonly begin at the calyx or at wound sites. Ensure good air circulation within the crop, maintain the relative humidity in the greenhouse below 85% and avoid the formation of free water on the plants and fruit (Howard et al 1994, Lange and Tantau 1996).

Powdery Mildew

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Powdery mildew of greenhouse pepper, caused by Leveillula taurica, is not a common problem in Canada. The first report of this disease in Canada was in 1999 in two separate greenhouse

locations in Leamington and Vineland, Ontario (Cerkauskas et al 1999). Yield losses of 10 to 15% were associated with the disease in these greenhouses (Cerkauskas et al 1999). Spots with a white powdery coating develops on the lower surface of the leaves, a slight chlorosis of the upper leaf surface is associated with the spots (Cerkauskas et al 1999).

Diseases of Sweet Pepper - Virus DiseasesPepper Mild Mottle Virus (PMMV)

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Pepper mild mottle virus occurs practically everywhere that pepper is grown and was first reported in Canada on field grown peppers in 1985 (Howard et al 1994). The first confirmed report of this virus in Alberta greenhouse sweet peppers was in 1998 (Calpas 1998). The presence of the virus is difficult to detect in the greenhouse until the plants begin to bear fruit. Leaf symptoms are easily mistake for other problems such as magnesium and manganese deficiencies. As the disease progresses in the plants, the new growth can be distinctly stunted with a clear mosaic pattern of yellow and green. Fruit symptoms often occur well in advance of the stunting symptoms and include the development of obvious bumps on the fruit as well as color streaking and green spotting as the fruit matures to color. Fruit tend to have pointed ends and may also develop sunken brown areas on the surface (Howard et al 1994).

Routine use of skim milk (100 gms / 1 Liter) as a dip while handling the plants acts to prevent any potential spread of the virus in the crop. The protein in skim milk binds to the virus and inactivates it. The virus is very stable in plant sap and it is easily spread from plant to plant. Once the plants begin to bear fruit, PMMV infected plants are fairly easy to recognize from symptoms on the fruit. Infected plants should be carefully removed and destroyed as the virus can survive in dry plant debris for up to 25 years (Portree 1996). If all

Figure 49. Pepper mild mottle virus symptoms.

plants bear normal fruit, dipping the hands in skim milk can be discontinued.Pepper mild mottle virus enters the greenhouse primarily on infected seed, transplants, plant sap and plant debris (Howard et al 1994, Portree 1996). The virus is not known to be spread by insects, but is very easily spread the routine handling of the young plants, especially at transplanting (Portree 1996). Many other plants in the Solanaceae family are susceptible, but tomato is not a host of PMMV. Pepper mild mottle virus is related to tobacco mosaic virus (TMV) and pepper cultivars with TM resistance also have a level of resistance to PMMV (Howard et al 1994, Portree 1996).

Tobacco Mosaic Virus (TMV)

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Tobacco is not a common disease problem in Canada although it occurs on greenhouse pepper throughout the world (Howard et al 1994, Portree 1996). The symptoms of infection first appear on the leaf as a necrosis along the main veins accompanied by wilting and leaf drop (Howard et al 1994, Portree 1996). New growth on the plants may exhibit mosaic symptoms as well as distorted growth (Howard et al 1994, Portree 1996). Use disease-free seed and ensure that resistant cultivars are grown. Use a skim milk dip when handling the plants and remove and destroy any infected plants that develop early in the season (Howard et al 1994, Portree 1996). Mature plants can be symptomless carriers of the virus and escape detection later in the season (Portree 1996).

Tomato Spotted Wilt Virus (TSWV)

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Tomato spotted wilt virus has a wide host range, affecting approximately 300 species in 34 families of plants (Howard et al 1994). The virus is spread primarily by thrips, particularly the western flower thrips (Frankliniella occidentalis), and will only become a significant problem in greenhouse pepper crops if the thrips vector is present (Howard et al 1994).

Figure 50. Tomato spotted wilt virus symptoms.

Symptoms of infection on the leaves includes blackish-brown circular spots, or tan spots bordered by a black margin (Howard et al 1994). Symptoms on ripening fruit are quite dramatic with orange to yellow spots surrounded by a green margin, or green spots on a background of the ripe fruit color of red, yellow or orange. Not all fruit from infected plants may develop fruit symptoms, experience in Alberta pepper greenhouses has shown that only about one-third of the fruit from infected plants will develop symptoms.

Control of this virus is obtained by controlling the thrips vector. Thrips biocontrol programs should be initiated at the beginning of the season. Weeds should be kept under strict control as they can serve to harbour both the thrips vector and the virus. Maintaining a 6 meter weed-free buffer

zone around the greenhouse will help prevent the introduction of thrips into the greenhouse, as well as preventing the establishment of virus infected weed plants around the greenhouse which could serve as a source of the virus. Avoid having any ornamental plants in the greenhouse as they can also serve as reservoirs for the virus.

Tomato Mosaic Virus (ToMV)

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Tomato mosaic virus is not a common problem in greenhouse pepper and causes symptoms very similar to those caused by tobacco mosaic virus (Howard et al 1994). Control measures are the same as for tobacco mosaic virus. Use disease-free seed and remove and destroy infected plants (Howard et al, 1994).

Diseases of Sweet Pepper - Physiological DisordersBlossom End Rot

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Blossom end rot (BER) is a common disorder of greenhouse peppers, with the symptoms occurring on the pepper fruit. The disorder is associated with a number of environmental stress triggers as well as calcium deficiency (Howard et al 1994). Any condition which causes water stress or a reduction in transpiration, and resultant movement of nutrients through the plants can bring on symptoms. Under watering, fluctuating water conditions, from dry to wet to dry etc., damage to the root system high E.C. in the root zone can cause BER (Howard et al 1994, Portree 1996). An actual calcium deficiency to the plant is rarely the primary cause of the disorder as BER can develop when adequate levels of calcium are being fed to the plants. The environmental factors that can trigger the disorder interfere with the movement of calcium within the plant, causing less calcium to reach the fruit. Some cultivars are more prone to this disorder than others (Portree 1996).

Symptoms of BER begin as soft spots on the fruit which develop into sunken tan-brown lesions with a very distinct border between affected and healthy tissue. The spots usually occur on the bottom third of the fruit and

Figure 51. Blossom end rot.

are not strictly confined to the bottom, or blossom end of the fruit. Affected fruit are unmarketable. Control is obtained by avoiding conditions of moisture stress or conditions of reduced transpiration in the crop, ensure that the plants receive adequate water and that vapor pressure deficit (VPD) targets are met. Weekly foliar applications of calcium nitrate can have a significant impact on reducing the amount of BER ( Schon 1993).

Sunscald

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

The symptoms of sunscald on the pepper fruit are very similar to those for blossom end rot. Soft, tan coloured sunken lesions develop fruit that are exposed to direct sunlight. It is important to adjust pruning practices to ensure that all fruit are shaded from direct sunlight. Applying shading to the greenhouse during the summer months will also help reduce the incidence of sunscald. Temperatures of exposed fruit can often be 10 °C higher than shaded fruit, reaching over 35 °C during the mid day of a typical hot, sunny Alberta afternoon, even when air temperatures in the greenhouse are maintained below 27 °C. Fruit temperatures over 35 øC should be avoided (Portree 1996).

Figure 52. Sunscald.

Fruit cracks

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

This condition is characterized by the appearance of very fine, superficial cracks on the surface of the pepper fruit which gives a rough texture to the fruit (Portree 1996). The development of these cracks are associated with sudden changes in the growth rate of the individual fruit. The appearance of fruit cracks can follow periods of high relative humidity (over 85%), changes from hot sunny weather to cool cloudy weather or vise versa (Portree 1996). Maintaining a consistent, optimized growing environment is the best way to prevent the development of fruit cracks.

Fruit Splitting

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

The development of large cracks in the fruit is a direct response to high root pressure. Factors that contribute to the development of high root pressure directly impact fruit splitting (Portree 1996). Ensure that optimal VPD targets are met at all times. Adjust the timing of the last watering in the day so as not to water too late. Eliminate any night watering cycles.

Fruit Spots

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

The appearance of small whit dots below the surface of the pepper fruit is associated with excess calcium levels in the fruit, and the subsequent formation of calcium oxalate crystals (Portree 1996). Conditions that promote high root pressure will also favor the development of fruit spots.

Misshapen Fruit

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

The development of misshapen fruit is generally associated with sub-optimal growing conditions at flowering and pollination which result in poor flower development or poor pollination. Section 6.3.7 discusses some of the common causes of misshapen fruit, which include the temperatures being either too cool or too warm. Ensuring that all environmental targets are met and maintained will reduce or eliminate the development of misshapen fruit.

Figure 53. "Wings" on pepper fruit due to lowtemperatures during pollination.

Internal Growths in the Fruit

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

The development of growths within the pepper usually appear early in the cropping cycle, generally on the first fruit set (Portree 1996). This results from abnormal tissue development in the honey gland of the fruit (Portree 1996).

Appendix IEffect of Pesticides on Biological Control Agents*

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Trade Name Common Name Encarsia

Aphidius

Persimilis Fallicis

Cucumeris Hypoaspis3 degenerans

Aphidoletes Orius Harmonia Delphastus

Admiral* pyriproxifen H(35)N I I H(7) H(7)

Admire* imidacloprid H(21)N S S H(21) H(21)

Afugan pyrazofos H(21) S(0) H(1) H(21) H(21)

Agrimycin streptomycin S S S S S

Ambush* permethrin H(56)N H(56) H(56) H(56) H(56)

Apex methoprene S S S S ?

Applaud buprofezin H(3) I(0) S H(7) H(3)

Avid* abamectin H(21)R H(14) H(14) H(21) H(14)

Azatin azadarachtin ? S ? ? S

B-Nine daminozide S S S S ?

Baygon propoxur H(60)N H(14) H(42) H H

Basamid dazomet S S S S S

Benlate, S benomyl S H(14) H(14) S H

Botran DCNA S S S S S

Bravo chlorothalonil I(7) S I S S

Captan captan S S S S S

Citation cyromazine S S S H I(7)

Cygon* dimethoate H(60)N H(60) H(60) H(14) H

Daconil chlorothalonil S S I S S

DDVP dichlorvos H(7) H(3) H(3) H(3) H(7)

Decis* deltamethrin H(56)N H(56) H(56) H(56) H(56)

Derris rotenone H(42)N H H H(14) H

Diazinon* diazinon H(42)N I(7) H(21) H(42) I

Dibrom F naled H(7) H(3) H(3) H(7) H(3)

Dimilin diflubenzuron S S S S S

Dipel Bacillus Thuringiensis

I S S I I

Dithane Maneb I S S I H

Dursban chlorpyrifos H(28)N H(3) H(14) H(28) H(28)

Dyno-mite pyridaben H(29)N H H H(28) H(14)

Enstar kinoprene I I I I I

Epsom salts MgS04 S S S S S

Exotherm chlorothalonil I(7) S S S S

Fixed copper

copper I(7) S S S S

Formalan formaldehyde H H H H H

Fungaflor imazalil S H(3) S H(3) S

Gardona* tetrachlorvin-

-phos H(56) I H(42) H(42) H

Insecticidal

- soap

fatty acid salts

H(0) H(0) H(0) H(0) H(0)

Impower* imidacloprid H(21)N S S H(21) H(21)

Karathane dinocap H(7) S I H(7) ?

Kelthane dicofol H(7) I(14) H(30) H(4) I

Kumulus sulphur H(28)N I(7) I(7) I I

Lannate* methomyl H(48)N H(21) H(42) H(56) H(56)

Lindane* lindane H(56)N H(42) H(42) H(56) H

Lorsban chlorpyrifos-

-methyl H(42)N H(7) H(42) H(7) H

Malathion* malathion H(56)N I(7) H(56) I(20) H

Manzate mancozeb I I S S S

Maltatox dodemorph I(7) S I(7) I I

M-Systox-R*

oxydemeton

methyl H(56)N H(7) H H ?

Micro-Niasul

sulphur H(7) I I I I

Mitac amitraz H(21)N H(21) H(21) H(14) I(21)

Morestan oxythiioquinox I H(14) H(14) I ?

Monitor* methamidophos H(28)N H(56) H(20) H(21) H(21)

Nicotine nicotine I(7) H(7) H(7) H(I) H

Nimrod bupirimate S I(4) S S I(0)

Nova mycobutanil S S S S I

Oil refined oils H(0) H(0) H(0) H(0) H(0)

Omite propargite I(7) H I I

Orthene* acephate H(56)N H(14) H(56) H(56) H(42)

Paration F* parathion H(56)N I(5) H(42) H(56) H

Phosdrin mevinphos H(7) I(7) H(7) H(7) H

Pirliss pirimicarb I(7) I I H(7) I(3)

Plantfune 103*

sulfotep H(70)N H(70) H(70) H(70) H

Pyrethrum pyrethrins H(7) H(7) H(7) H(7) I

Ridomil metalaxyl S I I S ?

Rovral iprodione S S S S S

Rubigan fenarimol S S S ? S

Sevin* carbaryl H(28)N H(14) H(30) H(30) H

Sulfur F sulphur H(28)N S I(7) I I

Sulfur sulphur I I(7) I(7) I ?

Temik* aldicarb H(49)N H(21) H(21) H(49) H

Thiodan endosulfan H(4) H(14) H(4) H(14) H

Thiram thiram I(14) I(2) I(2) I(2) I

Trumpet bendiocarb H(21)N H(21) H(21) H(21) H

Trounce fatty acids + pyrethrin

I(7) I I I(7) I(7)

Vendex fenbutatinoxide S I S S S

Vydate* oxamyl H(56)N H(56) H(56) H(56) H(56)

Zineb zineb S S S I I

1. H(3) = harmful for # days, I = intermediate, some survival and reproduction, low residual effect, S = safe or negligible effect, ? = no data, presume toxic. 2. Applications are all foliar sprays unless indicated as F = fumigant, FS = floor spray, or DR = drench. 3. Spray will affect foliage-inhibiting Cucumeris more than the soil dwelling Hypoaspis. 4. N = Not normally compatible with bees and biologicals. Contact your supplier before using. 5. * = Do not use even for cleanup as residues may harm biological control agents for 12+ months as it may be absorbed in greenhouse poly or plastic coverings and insulation. *Reprinted with permission from Don Elliot, Applied Bio-Nomics Ltd.

Appendix IIPlant nutrient deficiency symptoms

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

Nitrogen Plant light green with lower leaves yellowing, slow growing.

Phosphorus Plant dark green, developing a purplish color, slow growing, stunted.

Potassium Chlorosis developing at leaf tips, moving down the edges of the leaves and between the veins, symptoms developing on lower leaves first.

Magnesium Interveinal chlorosis beginning on older leaves, chlorotic patches developing to be fairly large, 0.5 - 0.75 mm in diameter. Can also develop a reddish-purple hue at the margins of the chlorotic spots.

Calcium Deficiencies occur at growing points, young developing leaves at the terminal buds develop a "hooked" appearance at the tips, later leading to browning (tip burn) and die-back. Increased severe blossom end rot (BER) of fruit.

Sulfur Plants light green in color over entire plant, symptoms can be confused with nitrogen deficiency. Nitrogen deficiency initially affects the older leaves first.

Iron Interveinal chlorosis of young leaves, veins remain green giving a finely netted appearance to the leaves. Interveinal chlorosis will eventually spread to the older leaves.

Manganese Interveinal chlorosis of young leaves. Manganese deficiency is difficult to distinguish from iron deficiency based on visual symptoms.

Copper Young leaves permanently wilted, unable to stand erect. Eventually the growing point browns and dies.

Zinc Interveinal chlorosis of new leaves that produces a "banding" appearance. As the condition progresses the new internodes shorten producing a rosette appearance at the tops of the plants.

Molybdenum Deficiency symptoms resemble nitrogen deficiency symptoms, older and middle leaves become chlorotic first. Margins of the leaves can develop a curled appearance, formation of flowers is restricted.

Boron Abnormal development of growing points, eventually becoming stunted and die.

Chlorine Chlorosis of younger leaves and wilting of the plant and overall wilting of the plant.

Bibliography

Guide to Commercial Greenhouse Sweet Bell Pepper Production in Alberta

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This information is maintained by James Calpas Last Revised/Reviewed March 7, 2001