Pest Management for Vegetable Bedding Plants
Vegetable bedding plants are commonly grown in the Northeast as part of the spring sales mix or for field setting. Although vegetable bedding plants may only be in the greenhouse for a short period of time, it is important to produce a high quality pest-free transplant. This can pose a challenge. A review of pesticide labels indicates that there are few growth regulators (Note: Sumagic uniconazole) is labeled as a foliar spray on vegetable transplants) and only a limited number of insecticides and fungicides labeled for greenhouse-grown vegetable bedding plants.
Integrated pest management (IPM) offers a practical way to effectively manage pests on vegetable bedding plants. Through the use of sound cultural practices, monitoring techniques, accurate problem identification, and timely implementation and evaluation of appropriate management strategies, growers can improve vegetable bedding plant production while minimizing their reliance on routine pesticide applications. IPM utilizes many different management options; cultural, physical, mechanical, biological and chemical. Routine crop inspection alerts growers to developing pest and cultural problems while they are still minor and can be easily managed. Early detection and intervention is the foundation of an IPM program.
To begin, obtain up-to-date cultural information and schedules for producing vegetable bedding plants. Grow the crops at appropriate temperatures. Many Cole crops such as cabbage, broccoli, and cauliflower may "button" or flower prematurely, if grown at too low of a temperature. Vegetable bedding plants also benefit by a gradual “hardening” off period before they are transplanted into the field. Gradual exposure to outdoor growing conditions and reduced watering at the end of the growing period help to toughen the young plant. Consult with your seed supplier or review the references listed at the end of this fact sheet for information specific to the crops you will be growing. Pay particular attention to scheduling times, light, temperature and nutritional requirements needed to grow healthy transplants.
Managing Plant Height
Since very few growth regulators are registered for vegetable bedding plants, plant height is managed by adjusting water, temperature and fertilizer levels, or by physically brushing the plants. Research has shown that mechanical stress reduces stem elongation and maintains plant height. For example, brushing transplants twice daily for 18 days using about 40 strokes back and forth with a cardboard tube suspended from an irrigation boom can result in as much as a 30% reduction in stem elongation. Growers have also successfully used a wand made of plastic plumbing pipe or a flat piece of polystyrene foam. Vegetable plants such as tomatoes, eggplants and cucumbers have responded to this method of height control. Note that this technique has damaged some tender plant species such as peppers and could also enhance the spread of disease.
Water stress is another tool growers can use to manage plant height. Maintaining plants on the dry side limits cell expansion and plant growth. This method requires close attention to avoid permanent damage such as leaf burn or even plant death. One technique is to irrigate the growing mix thoroughly and then allow it to dry to the point where plants wilt before irrigating thoroughly again. Growth is restricted during the period when the growing medium is very dry. Once watered, the plants rapidly resume growth. Experienced tomato growers have successfully used this technique.
Withholding nutrients can also be used to prevent stretching. Low phosphorus fertilization is especially effective for tomatoes. If carefully managed, a mild to moderate phosphorus (P) deficiency may result in a desirable reduction in growth with no foliar symptoms of P deficiency. See section on fertility for more information.
Diseases of vegetable bedding plants include Botrytis blight, damping-off, powdery mildew,tospoviruses and bacterial diseases such as bacterial leaf spot, bacterial canker, and black rot. To effectively control diseases, it is important to properly identify them. When diseases are not successfully managed, it is often because the cause was not accurately identified. Symptoms caused by poor cultural practices can also mimic disease symptoms. Fungicides cannot correct problems caused by high soluble salts, poor aeration or a nutrient imbalance. An integrated approach to disease management involves the use of resistant cultivars, sanitation, sound cultural practices and the proper use of the correct pesticide.
Seed catalogues often feature disease resistant and tolerant varieties of vegetables. Utilize resistant varieties where feasible, but take some time to research the diseases that are giving you the most trouble to find other strategies to incorporate into the disease management plan.
There are three kinds of media that are generally used for greenhouse potting mixes and seedling flats: soilless media, compost or a mixture of a small percentage of field soil and soilless media. Soilless media is generally purchased in bags or custom mixed on-site and contains no field soil. Soilless media purchased in bags does not have to be treated before use. Preventative applications of one or several fungicides or biological fungicides may be necessary with some crops that are prone to damping off.
Field soil, whether to be used by itself or as an amendment in a soilless medium, must be treated to eliminate soil-borne plant pathogens, insects, and weed seeds. Once the soil has been treated, take care to avoid re -infestation.
Treatment of soil with steam is preferred over chemicals because it is very effective and safe. All pathogens will be killed by steam and only a few of the hardiest weed seeds will survive. There are portable steam generators available.
Ideally, the temperature of the entire soil mass should be raised to 160° to 180°F for 30 minutes. It is important to use several accurate thermometers placed in one or more corners and the center of the soil. Since it is difficult to avoid the soil temperature rising to 212°F, bring it up to this level and then reduce the pressure to allow the temperature to drop to 180°F in the coldest part of the soil mass.
The soil moisture content prior to steaming is important. Overly moist soil will take a long time to reach proper temperature. However, some moisture is necessary for the effective killing of microorganisms as well as the conductance of heat. Proper soil moisture for steaming is approximately the same for good planting conditions; soil squeezed in the hand should crumble easily. If possible, the soil mass should be moistened evenly two to three weeks prior to treatment. This will germinate difficult-to-control weed seeds, such as oxalis and clover, making them susceptible to heat.
Prolonged steaming of soil at temperatures higher than 180°F can result in undesirable side effects such as overkill of beneficial soil micro flora and accumulation of ammonium and manganese. Soil high in organic matter should be tested for ammonium after steaming. Several weeks may be necessary to allow for the dissipation or conversion of the ammonium. The incorporation of dolomitic lime and super phosphate, based on a soil test, may reduce ammonium levels.
Pest management on vegetable bedding plants begins with a clean, weed-free, disinfected greenhouse. Before growing the crop, the greenhouse should be cleared of plant debris, weeds, flats and tools. Empty benches, potting tables, storage shelves, tools and cell packs should be washed and disinfected with a sanitizing agent. After the greenhouse has been sanitized, care must be taken to avoid recontamination with pathogens. Purchase seed from reliable sources. If possible, purchase seed that has been disinfested by chemical and/or heat treatment by the seed company. Potting media is easily reinfested by dirty hose nozzles or tools and unsanitary growing conditions. The floor of the greenhouse is a good source for diseases. Use a hook to keep the hose nozzles off the floor. Grow transplants off the ground in a well-ventilated greenhouse. To prevent root rot diseases, avoid over -watering and over -fertilizing. Water early in the day to help prevent foliar diseases.
Use separate greenhouses for vegetable seedlings and ornamental bedding plants. Separate greenhouses:
will protect vegetable seedlings from any insect pests that may migrate from ornamentals and plants that are held over;
will protect vegetable seedlings from tospoviruses ; protect cucurbit seedlings from powdery mildew on verbena
will make it easier to treat the vegetable seedlings if pesticides are needed.
Techniques to reduce high humidity
High relative humidity is one of the major contributing factors to Botrytis blight, a common fungal disease of bedding plants. Warm air holds more moisture than cool air. During warm days, the greenhouse air is more humid. As the air cools in the evening, the moisture-holding capacity drops until the dew point is reached. Water then begins to condense on surfaces. Humidity can be reduced by exhausting the moist air and replacing it with cooler outside air that is drier. Activate the exhaust fans for a few minutes and then heat the greenhouse to raise the air temperature. Then, exhaust the humid air. The cooler, outside air will lower humidity levels as it is warmed in the greenhouse. A relay may be needed to lock out the furnace or boiler until the fan shuts off so that flue gases are not drawn back into the greenhouse. This will help to prevent air pollution damage to sensitive seedlings. Heat and vent two or three times per hour in the evening after the sun goes down and early in the morning at sunrise.
Using horizontal airflow (HAF) can also reduce condensation. HAF fans keep the air moving in the greenhouse, helping to minimize temperature differentials and cold spots where condensation occurs. Air that is moving is continually mixed. The mixed air along the surface does not cool below the dew point so does not condense on plant surfaces.
In addition, cultural practices can be used to reduce humidity within the plant canopy. These include proper watering practices and spacing of plants. Since most vegetable bedding plants are grown in flats that are spaced flat to flat, reducing humidity within the canopy is difficult. Proper planting dates, plant nutrition, watering practices and height management techniques help to prevent lush, overgrown plants thereby reducing humidity within the canopy.
Hand watering and overhead irrigation systems are the primary methods of watering vegetable bedding plants. Always water in the morning to reduce the length of time the leaves stay wet after irrigating to prevent foliar diseases. Rising temperatures during the day will evaporate water from the foliage, so the leaves stay dry. Avoid watering late in the day or when water will sit on leaf surfaces for long periods of time.
Seed treatments are useful for many vegetable crops to prevent root diseases, as well as certain diseases carried on or within the seed. There are two general types of seed treatment: eradicative and protective. Eradicative seed treatments use hot water or chlorine to kill disease-causing agents on or within the seed. They are useful in controlling certain seed-borne diseases such as bacterial leaf spot on pepper and bacterial canker on tomato. Protective seed treatments use fungicides on the seed surface to protect the seed against decay and soil-borne organisms such as damping off. For more information regarding seed treatments, contact your seed sales representative, Extension vegetable specialist or plant pathologist.
Fungicides can provide excellent management of some diseases, but for others they may be ineffective. In general, to control root diseases, broad-spectrum fungicides should be applied as a drench on a preventative basis. Read directions for application on pesticide labels. An application of additional water may be necessary. For foliage diseases, obtain thorough spray coverage and treat when disease is first evident. Table 2 provides a listing of fungicides labeled for vegetable bedding plants.
Biofungicides are biological fungicides that contain living organisms such as fungi, bacteria or actinomycetes (a group of bacteria that form branching filaments) that attack plant pathogens and the diseases they cause. They can be used as part of an integrated disease management program to reduce the risk of pathogens developing resistance to traditional fungicides. Currently, there are no pathogens that are resistant to biological fungicides.
Biological fungicides may suppress diseases in a number of different ways. They may directly compete with the pathogen. The biological fungicide “shields” the roots by growing a defensive barrier around the roots. Or the biological fungicide may produce an antibiotic or another toxin that kills the target organism. It may attack and feed upon the pathogen. As such, the biological fungicide must be present at the same time or before the pathogen appears. Some biological fungicides induce the plant to turn on their own defense mechanisms.
Some of the advantages of using biological fungicides include: lower Re-entry interval (REI) than traditional fungicides, may be OMRI listed, may be less phytotoxic, and many can be used in rotation with other chemicals. (See company web sites for more information on compatibility).
Biofungicides should be used as a preventative treatment in conjunction with a regular monitoring program where root health and crop quality is evaluated. They will not cure diseased plants and must be applied before the onset of the disease. Biological fungicides need to be used in conjunction with standard cultural practices that are used to help prevent diseases. Storage conditions, soil and air temperatures, and use of other chemicals affect their efficacy. Most biological fungicides also have a limited shelf life of one year. A number of products are commercially available for use on vegetable bedding plants. See Table 2 for information on labeled crops and diseases for bio logical fungicides.
Botrytis can cause leaf blight, cankers, damping off and root rot. Plants may be attacked at any stage, but the new tender growth, freshly injured tissues and dead tissues are most susceptible.
Symptoms: Botrytis blight produces characteristic gray fuzzy appearing spores on the surface of infected tissues. Air currents and splashing water can easily disseminate the spores. In general, germination of spores and infection is dependent on a film of moisture for 8 to 12 hours, relative humidity of 93% or greater and temperatures between 55° and 65°F. After infection, colonization of plant tissues can occur at temperatures up to 70°F.
Management: Management of environmental conditions such as temperature, humidity and duration of leaf wetness, sound cultural practices and fungicides will help prevent disease development.
· Control weeds and remove plant debris between crop cycles and during production. Dispose of diseased plants and debris in a plastic trash bag. Keep the bag closed to help prevent spreading spores to uninfected plants as the bag is removed from the greenhouse. Cover trash cans to prevent the airborne spread of spores from diseased plant tissue.
· Reduce humidity and leaf wetness duration to prevent spore germination. See techniques for reducing relative humidity.
· Provide good air circulation and reduce humidity within the canopy. Proper planting dates, fertility, watering and height management will prevent overgrown plants, thereby reducing humidity within the canopy.
· Water in the morning, never late in the day. Rising temperatures during the day will cause water to evaporate from the foliage and dry the leaf surface.
· Avoid growing ornamental hanging baskets above vegetable bedding plants. Spent flowers dropping on plants below cause Botrytis infection.
Damping-off of Seedlings
Damping-off is a common disease of germinating seeds and young seedlings. Several fungi are capable of causing damping-off including Rhizoctonia, Alternaria, Sclerotinia and the water molds, Phytophthora and Pythium. Soil-borne fungi generally do not produce air-borne spores but are easily transported from contaminated soil to pathogen-free soil by infected tools, hose ends, water-splash and hands. Young seedlings are most susceptible to damping-off. However, later in the crop cycle, the same pathogens may cause root and stem rot.
Symptoms: Symptoms of damping-off include seedlings failing to emerge or wilting, often with a stem lesion that appears water-soaked or dark, necrotic and sunken at the soil line. The fungus disease usually spreads radically from a central point of origin so plants often die in a circular pattern. Vegetable seeds that are germinated in poorly drained, cool soils are especially susceptible. Young plants that do emerge are weak and often wilt at or below the soil line. Cabbage, cauliflower, tomato and pepper seedlings may be girdled by brown or black sunken cankers. Stems of these plants may shrivel and become dark and woody ( wire stem or collar rot). The plants may not collapse, but remain stunted and die after transplanting.
Management: Damping-off must be prevented because it is difficult to stop once symptoms occur. There are several strategies to prevent damping-off.
· Use only certified disease-free seed from reputable seed companies.
· Use fungicide-treated seed. Certain fungicides are labeled for damping-off for selected vegetable crops.
· Use pasteurized soil, compost-based or soilless mixes.
· Disinfect all flats, cold frames, pots and tools.
· Germinate seed under conditions that will ensure rapid emergence, such as with the use of bottom heat.
watering, excessive fertilizer, overcrowding, poor air
circulation, careless handling, and planting too deeply.
· Fill flats with pre-moistened growing media to avoid compaction.
· Lightly fill and brush containers.
· Do not pack young plants into containers, use pre-dibbled holes for transplants.
· To avoid compaction, do not stack or “nest” filled trays or pots.
· Provide adequate light for rapid growth.
· Promptly rogue out infected plants from flats.
Powdery mildew may occasionally occur on vegetable transplants including tomato, eggplant and other solanaceous crops, as well as cucurbit crops. Powdery mildew, unlike many foliar diseases, does not need free moisture on the leaf to thrive. Favorable environmental conditions include high relative humidity (greater than 95%), moderate temperatures of between 68 ° to 86° F and relatively low light levels. Infections may be more common in the spring when changes between the day and night temperatures encourage high relative humidity levels, especially at night.
Spores (conidia) are produced in chains. Air currents and water splash in the greenhouse easily move these spores. The spores germinate and thread-like strands (hyphae) grow along the leaf tissue. Powdery mildews obtain plant nutrients by sending feeding organs (haustoria) into the epidermis. Once a spore lands on a plant, it may take as little as 3 days but more often five to 7 days for infection to develop.
Symptoms : Powdery mildew is easily recognized by its white talcum-like growth. Faint, white mycelium may develop on leaves and stems, with yellow margins . When symptoms develop on the more mature leaves, powdery mildew is harder to detect and seems to occur “overnight”, catching many growers unaware. As soon as favorable environmental conditions develop, powdery mildew develops into an epidemic as more leaves become infected.
· Maintain proper plant spacing to reduce relative humidity levels within the plant canopy. (This will also help you gain better spray coverage).
· Keep relative humidity levels below 93 percent in the greenhouse. Heat and ventilate in the late afternoon and early morning to reduce high relatively humidity at night.
· Clean your greenhouse thoroughly between crops, removing all weeds that could be potential hosts.
· Greenhouse growers who produce cucurbit transplants as well as verbenas should be especially careful to separate these two crops. It is possible that this powdery mildew could affect the cucurbit transplants that may not have otherwise become infected until the fruit was beginning to form in the field. The powdery mildew that affects certain cultivars of ornamental verbena can also infect cucurbit seedlings including squash, cucumbers and pumpkins.
Tospoviruses are a group of viruses that include impatiens necrotic spot virus (INSV) and tomato spotted wilt virus (TSWV). They may infect hundreds of plant species including tomatoes, peppers and eggplant. These viruses are primarily spread by the western flower thrips. Tospoviruses are not seed-borne but are brought into the greenhouse on vegetatively propagated ornamental plants or seedlings that have been exposed to the virus. Once the thrips in the greenhouse become infected, they can transmit the virus to susceptible crops and weeds.
Symptoms: Symptoms include stunting, foliar ring spots and black lesions on stems. Symptoms of INSV and TSWV will vary depending upon the host.
Management: To manage tospoviruses, it is necessary to discard infected plant material, including weeds and to manage thrips. Infected vegetable transplants planted into the garden or field will be stunted and will not produce a harvestable crop. Since INSV and TSWV are not seed-borne, vegetable transplants may be kept free of tospoviruses if they are not brought into contact with other infested crops or thrips carrying the virus. Growers attempting to concentrate all their warm temperature crops in a single house run a risk of mixing tospovirus-free vegetable seed crops with leftover ornamental stock plants or new cuttings that may carry the virus. Pre-finished or vegetatively propagated ornamentals from another producer could be infested with thrips or infected with a virus. Therefore, vegetable bedding plants should always be grown in separate greenhouses.
Bacterial diseases of vegetable bedding plants, such as bacterial leaf spot of peppers, bacterial speck and bacterial canker of tomatoes and black rot on Cole crops are introduced into a greenhouse through infected seed and transplants.
Bacterial leaf spot, Bacterial speck
Symptoms: Bacterial leaf spot is caused by Xanthomonas campestris pv. vesicatoria and is found primarily on peppers although all aboveground parts of tomatoes are also susceptible. Spots on leaves are chocolate-brown and irregularly shaped with areas of dead leaf tissue. At first, the spots are less than 1/4 of an inch in diameter. Severely spotted leaves will appear scorched and defoliation may occur. This disease is most prevalent during moderately high temperatures and long periods of leaf wetness.
Bacterial speck occurs on tomato but not pepper. The bacterium, Pseudomonas syringae pv. tomato, causes small black spots to develop resulting in chlorosis (yellowing), necrosis (dead tissue) and blighting of the foliage. Bacterial speck can usually be distinguished from bacterial spot by the size of the lesions, however, in some cases, the symptoms look similar.
Bacterial canker of tomato is caused by Clavibacter michi-ganensis (formerly Corynebacterium michiganense). In New England, bacterial canker occurs less frequently than other tomato diseases but it is potentially more destructive. The bacterium is seed-borne but may survive on plant debris in soil for at least one year. It can also survive in the greenhouse on wooden stakes and flats. Wilt, leaf scorch, canker, pith necrosis and fruit spot may occur singly or in combination depending on the circumstances. When the bacterium is carried in the seed, the vascular system becomes colonized, resulting in wilt, pith necrosis and external cankers. Wilt initially occurs on one side of a leaf or one half of a plant because only a portion of the vascular system is blocked. Cankers and pith necrosis occur in later stages of disease development. Cankers are dark and water-soaked in appearance and often exude bacteria that are easily spread to adjacent plants. Pith necrosis is first evident as a darkening of the center of the stem that soon becomes chambered or hollow. When leaf scorch occurs, the petioles usually bend downward while the leaf edges curl up. The margins of the leaves become brown with a yellow border to the inside. Scorching of the foliage often develops in the absence of wilt or stem canker. Transplants may not express symptoms until six to eight weeks after infection and initial symptom expression is accelerated by environmental stress.
Black rot, caused by the bacterium Xanthomonas campestris pv. campestris occurs wherever cruciferous plants are grown. Cabbage, cauliflower and Chinese cabbage are often severely affected. The bacterium enters the leaves by colonizing the hydathodes (water pores) and moves from the leaf margins inward. Lesions may also begin at wounds. Diseased tissue is often V-shaped; flaccid, tan to yellow and with blackened veins. The blackened veins are diagnostic and are best seen by holding the leaf up to the sun. When the lesions reach the petiole and stem, the bacterium moves systemically through the plant, resulting in premature leaf drop. At this stage of disease, a cross-section of the stem will reveal a ring of discolored vascular tissue.
Management of bacterial diseases: These bacteria can be introduced on infected seeds, infected transplants purchased from another operation, or in the field on crop residues. These bacteria can also survive on weeds in the same family as the host crop. The management of these bacterial diseases is similar and includes the following strategies:
· Buy certified seed from a reputable source.
· Use hot water-treated seed. Ideally, the seed should be custom-treated by the seed company. Seed companies may treat the seed upon request. There is a risk that germination percentages will be reduced if the seed crop is grown under stressful environmental conditions.
· Promptly remove infected plants and adjacent plants to prevent further infection and avoid unnecessary handling of plant material.
· Avoid overhead irrigation, splashing or periods of extended leaf wetness.
· Disinfect all benches, equipment, flats and stakes.
· Follow sound practices for weed and insect control.
Prevent bacterial leaf spot on peppers by choosing resistant varieties whenever possible. There are many resistant varieties of bell peppers available, but there are few choices for resistant specialty peppers.
General Pest Management
A regular monitoring program is the basis of all pest management programs. Conduct a regular, weekly scouting program to detect problems early. This early detection and treatment will result in better pest control since plant canopies are smaller and better spray coverage can be achieved.
Yellow Sticky Cards
Use yellow sticky cards to trap and detect adult stages of fungus gnats, thrips and whiteflies. Place one to four cards per 1,000 square feet. The cards should be spaced equally throughout the greenhouse in a grid pattern with additional cards located near doorways and vents. Place some cards just above the plant canopy (to detect thrips and whiteflies) and some of the cards on the rim of the flats or pots to detect fungus gnats. Inspect and replace the cards weekly to keep track of population trends.
Plant inspection is needed to assess general plant health and to detect diseases, mites and aphids plus any hot spots of immature whiteflies. Randomly select plants at ten locations in an area of 1,000 square feet, examining plants on each side of the aisle. Start this pattern at a slightly different location each week, walking through the greenhouse in a zigzag pattern down the walkway. Examine the underside of leaves for insect pests and inspect root systems to determine whether they are healthy.
Key Plants and Indicator Plants
Focus on scouting key plants and indicator plants. Key plants are those plants or cultivars that have serious, persistent problems every year. For example, peppers , tomatoes and eggplants are prone to aphid infestations. Look for aphids on the young leaves and for shiny honeydew on the upper leaf surface. If grown near flowering plants, peppers, tomatoes and eggplant will also indicate an early thrips population. Look for distorted, young leaves with silvery flecked scars that are signs of thrips feeding damage.
Fava beans and certain cultivars of petunia are used as indicator plants to detect the presence of thrips carrying INSV and TSWV. These plants will develop viral symptoms within one week if fed on by the infected thrips. The petunia cultivar 'Summer Madness' and several varieties of fava bean have been successfully used to detect tospoviruses. To use petunias and fava beans as indicator plants:
· Remove flowers from indicator plants to encourage feeding on foliage where symptoms can be observed.
· Place a blue non-sticky card in each pot at plant height. The blue card will attract thrips to the indicator plant. Blue plastic picnic plates work well.
· Place petunia plants throughout the greenhouse among the crop at a rate of one plant every 20-30 feet and fava bean plants at the rate of 12 pots per 1,000 sq. ft.
· Remove symptomatic leaves on petunia plants and continue to use the plants. The virus is not systemic in these plants. Thrips feeding injury leaves distinct white feeding scars on the foliage. Virus symptoms appear as a brown rim around the feeding scars.
· Remove entire plants of fava beans if symptoms are observed, because the virus is systemic in these plants. Viral symptoms appear as dark brown angular lesions on leaves or yellow to light green ring spots. Dark necrotic areas can also be seen on the stem. Fava beans have dark black spots on their stipules that should not be confused with viral symptoms.
· Replace with new plants, planting 1-2 bean seeds per 4'' pot.
Record Keeping and Decision-Making
Each time the crop is scouted, record the pest numbers, their location and the number of plants inspected. Records on pest numbers and locations will help you identify population trends. Population trends will also indicate if initial control measures were successful or if they need to be repeated. Once this information is collected each week, a pest management decision can then be made. Monitoring and record keeping will answer the following questions and help you make the necessary treatment decisions. Is the population decreasing, increasing or remaining stable over the growing season? Do you need to spray? Are insects migrating from weeds under the benches to your crops? Is the treatment from last week working? Table 2 provides a list of selected materials labeled for managing insects, mites and diseases on greenhouse-grown vegetable transplants. Follow label instructions before using the material on vegetable bedding plants. The product must be used only for crops for which the compound is registered.
Biological Control for Insects and Mites
Biological control may be an option for aphids, mites, fungus gnats, thrips and whiteflies. Natural enemies are living organisms that need to be released when pest populations are low. They do not act as quickly as pesticides so cannot be used as a "rescue" treatment. Natural enemies (parasites, predators or pathogens) are best used early in the cropping cycle when plants are small, pest numbers are low and damage is not yet observed. A detailed plan of action is needed to insure success. Accurately identify the key pests in your production system. Natural enemies, especially parasites, are often very specific to a particular pest. Many insecticide residues can adversely affect natural enemies for up to 3 months after their application. Koppert Biological Systems has compiled a list of insecticides and their effects on natural enemies. This list is available from Koppert Biological Systems, Inc., 2856 South Main St., Ann Arbor, Michigan 48103 or through their website www.koppert.com. Biobest Biological Systems also has a searchable pesticide side effects database on their website . Become familiar with using insecticides that are compatible with natural enemies such as insecticidal soap, horticultural oil certain insect growth regulators and neem-based materials (azadirachtin products, see Table 1) and have a sprayer dedicated for their use.
Start in a small trial area to become familiar with releasing, monitoring and evaluating the effectiveness of natural enemies. A separate greenhouse is best. With help from your supplier and university specialist, establish a schedule for introducing the natural enemies. Release rates and timing will vary depending upon the crop and its size, the degree of infestation, effectiveness and type of natural enemies, plus the time of year. Starting a biological control program will involve some trial and error, as release rates have not been scientifically evaluated for vegetable bedding plants. Vegetable bedding plants with only one or two key insect pests or with a longer production schedule may be logical candidates for biological control. Be sure that natural enemies are received from your supplier quickly (2-4 days), and that they are kept cool during shipment. Inspect natural enemies for viability and quality when they are received. Table 3 provides information on scouting for key pests and biological control options.
Specific Insect Pests and Mites
Common insect pests on vegetable bedding plants include aphids, fungus gnats, shore flies, whiteflies, thrips and two -spotted spider mites. The following are brief descriptions, life cycles and monitoring tips for the major pests. See Tables 2 and 3, for additional scouting guidelines, registered pesticides and biological control options.
Lifecycle: Several species of aphids can occur on vegetable transplants, but the most common are green peach, melon and foxglove. Aphids are small, 1/16-inch in length, round, soft-bodied insects that vary in color from light green to pink or black. The green peach aphid is yellowish-green in summer; pink or yellowish in fall and spring. Winged forms are brown with a large dusky blotch on the abdomen. Melon aphids are greenish-yellow to very dark green with black mottling and short dark cornicles (tubular structures on the posterior part of the abdomen). Foxglove aphids are smaller than potato aphids but larger than melon and green peach aphids. The foxglove aphid is a shiny light yellowish green to dark green in color with a pear-shaped body. The only markings on the bodies of wingless adults are dark green patches at the base of the cornicle. The legs and antennae also have black markings. Foxglove aphids cause more leaf distortion than green peach or melon aphids. Aphids feed by inserting their piercing, sucking mouthparts into plant tissue and removing fluids. In greenhouses, aphids are usually females that produce live young called nymphs. Each female can produce 50 or more nymphs. Nymphs mature to adulthood and begin reproducing in as little as 7 to 10 days. Adults are usually wingless, but some will produce wings when populations reach outbreak levels. Large numbers of aphids will stunt and deform plants. In addition, aphids produce a sticky digestive by-product called honeydew. Honeydew can cover leaves and provide a food source for a superficial black fungus known as sooty mold. Aphids are present on weeds and may enter the greenhouse through vents.
Monitoring: Examine the foliage, along stems and new growth of key plants such as peppers ,eggplants , Cole crops and leafy greens to detect an early aphid infestation. Signs of aphid activity include shed white skins, shiny honeydew, curled new leaves, distorted growth and the presence of ants. Yellow sticky cards help detect the entrance of winged aphids into the greenhouse from outdoors. Yellow cards will not, however, allow you to monitor aphids within the crop, as most of the aphids will be wingless.
Lifecycle: The silverleaf whitefly (Bemisia argentifolii) and greenhouse whitefly (Trialeurodes vaporariorum) may infest vegetable bedding plants. However, greenhouse whitefly is the most common species. Both adult and immature whiteflies have piercing sucking mouthparts, are able to remove fluids and produce honeydew that also results in sooty mold fungus. Winged adult whiteflies are 1/16-inch in length, and found on the undersides of the youngest, most tender leaves. Females may lay from 150 to 300 eggs, which hatch into first-instar nymphs in about a week. The crawlers move for a short distance before settling down to feed. After three molts, a pupal stage is formed from which adults emerge in about six days. Whiteflies complete their egg to adult cycle in 21 to 36 days depending upon greenhouse temperatures.
Monitoring: To monitor whiteflies, check susceptible plants , such as tomatoes, at ten locations in an area of 1,000 square feet, examining plants on each side of the aisle. Look on the undersides of one or two leaves per plant, for nymphs, pupa and adults. Yellow sticky traps can also be used to detect adult whiteflies once populations have reached higher densities. Begin treatments as soon as the first sign of infestation is noted.
Fungus Gnats and Shore Flies
Lifecycle: The damp, moist environment in greenhouses favors both fungus gnats and shoreflies. Fungus gnat larvae are translucent, white and legless, about 1/4 inch long when mature, and have a shiny black head. The mosquito-like adult is about 1/8 inch long, with long legs, a pair of clear wings and long antennae. There is a distinct "Y" vein on each wing. Fungus gnats are weak fliers and are frequently observed resting on pot media or running over the foliage or other surfaces. The larvae feed on fungi and decaying organic matter, and often injure seedlings and plants. Larva feeding occurs on young, tender roots and in the stem at the base of the plant. This feeding injury provides an entry for disease pathogens. A female fungus gnat may lay up to 300 whitish eggs in clusters of 20 or more. The eggs are deposited on the surface or in the crevices of moist soil or potting media. Eggs hatch in about six days. Larvae feed for 12 to 14 days before changing into pupae. The pupal stage may last five to six days. Adults live up to ten days. The life cycle from egg to adult requires approximately three to four weeks depending on greenhouse temperatures.
Adult shore flies also occur in greenhouses and are confused with fungus gnats. The adult shore fly is about 1/8 inch long and has a robust body, very short antennae, shorter legs and dark wings with about five light spots. Larvae are off-white and do not have distinct head capsules. Shore flies do not injure plants through direct feeding, but can carry root rot pathogens from diseased to healthy plants. Their fecal spots or droppings can also be unsightly. To manage shore flies, control their food source, algae.
Monitoring: To monitor for fungus gnat larvae, place raw potato chunks with peel removed on the media surface. Larvae are attracted to the potato chunks, under which they move and congregate. Check the potato chunks after 2 days for larvae. Potato disks cut one inch in diameter and 0.5-1 inch thick work well. In addition, choose plants on each bench and inspect the soil surface and around the base of the plant including the stem just below the soil line. Record the location and the level of infestation. Badly infested plants should be removed as they serve as a source of infestation.
Adult flies can be monitored with yellow sticky cards placed at the base of the plant at soil line. Weekly inspections of yellow sticky cards can detect the onset of an infestation, and continued recording of the number of adults per card per week can aid in evaluating the efficacy of control efforts.
Lifecycle: The most injurious species is the western flower thrips (WFT). They often do considerable damage before they are discovered, because thrips are small, multiply rapidly and feed in plant buds in which they can remain undetected. WFT also vector tospoviruses. Feeding marks from the rasping mouthparts of thrips appear as white streaks on the leaves. Infested new growth may curl under and leaves are often deformed. Adult WFT are about 1/16-inch long, with narrow bodies and fringed wings. Females are reddish brown and males are light tan to yellow. The immature stages are light yellow. Female thrips insert eggs (several hundred per female) into plant tissue. The tiny yellowish larvae molt twice and feed on plant fluids as they mature. Larvae drop off the plant into the soil and pass through two stages, after which adults emerge. The egg to adult lifecycle can be completed in 7 to 13 days depending upon greenhouse temperature. During warmer temperatures development is more rapid than at cooler temperatures.
Monitoring: Early detection of a thrips infestation is critical for effective management because populations are lower and it is easier to obtain good coverage when plant canopies are small. Symptoms of their feeding are often not noticed until the damage has occurred. Eggplant, tomatoes, and peppers are especially prone to thrips infestations. Yellow sticky cards, key plants and indicator plants provide an easy way to detect the onset of an infestation. Yellow sticky cards should be placed just above the crop canopy, and near doors, vents and over thrips-sensitive cultivars to monitor the movement of thrips. Recent research has shown the light to medium-blue sticky cards catch more thrips than yellow ones. However, it is more practical to use yellow cards for general pest monitoring to attract fungus gnats, whiteflies and winged aphids. The number of thrips per card should be recorded and graphed weekly to monitor population levels and movement in or out of the greenhouse, and thus aid in control decisions. See section on key plants and indicator plants for more monitoring information.
Lifecycle: Two-spotted spider mites can be found on vegetable bedding plants. Adult females are approximately 1/50-inch long, and slightly orange in color. All mobile stages are able to pierce plant tissue with their mouthparts and remove plant fluids. Most spider mites are found on the underside of leaves. Feeding injury often gives the top leaf surfaces a mottled or speckled, dull appearance. Leaves then turn yellow and drop. Large populations produce visible webbing that can completely cover the leaves. Eggs are laid singly, up to 100 per female, during her 3 to 4-week life span. Eggs hatch into larvae in as few as 3 days. Following a brief larval stage, several nymphal stages occur before adults appear. Egg to adult cycle can be completed in 7-14 days depending upon temperature. Hot and dry conditions favor spider mite development.
Monitoring: Checking for mites must be done by examining foliage. Adult mites are not found on sticky cards. Mites often develop as localized infestations on particular groups of plants such as beans , tomatoes or eggplants. Sample plants by turning over leaves and with a hands-free magnifier (Optivisor) or hand lens, check for the presence of spider mites.
Life Cycle: The shiny, orange-tinted cyclamen mites prefer to hide in buds or deep within the flowers. Adult females can lay from 2 to 3 eggs per day for up to two to three weeks. Eggs are deposited in moist places at the base of the plant. Cyclamen mites can complete their life cycle in 1 to 3 weeks. Females can live up to one month and can reproduce without mating. Cyclamen mite females lay 2 to 3 eggs per day for up to two to three weeks. Cyclamen mite eggs are oval, smooth and about one half the size of the adult female. Larvae hatch from the eggs in 3 to 7 days. The slow moving white larvae feed for 4 to 7 days. Cyclamen mites prefer high relative humidity and temperatures of 60o F. Cyclamen mites feed upon many ornamental bedding plants including dahlia, fuchsia, gerbera daisy, petunias, viola as well as strawberries in the field. They may migrate to peppers or tomatoes.
Monitoring: Cyclamen mites pierce tissue with their mouthparts and suck out cell contents. Look for signs of damage which may be concentrated near the buds or occur on the entire plant. Symptoms include inward curling of the leaves, puckering and crinkling. Pit like depressions may develop. The mite is only 1/100 of an inch long. Examination under a microscope is often needed to confirm the presence of cyclamen mites.
Life Cycle: Broad mites are closely related to cyclamen mites. They can be distinguished from cyclamen mites by their egg stage. Eggs are covered with "bumps" that look like a row of diamonds. Eggs are best seen using a dissecting microscope. Adults and larvae are smaller than the cyclamen mites and walk rapidly on the underside of leaves. Broad mites can also attach themselves to whiteflies and use the whiteflies as a carrier for their dispersal. The development of broad mites is favored by high temperatures (70 to 80o F). Broad mites can complete their life cycle in as little as one week. Females lay from 30 to 75 eggs.
Monitoring: Broad mites can affect a number of ornamentals including gerbera daisy, New Guinea Impatiens, saliva, ivy, verbena and zinnia. They may migrate to peppers or tomatoes. Look for characteristic damage including leaf edges curling downward or terminal buds may be killed. As they feed, broad mites inject toxic saliva, which results in twisted, distorted growth. Do not confuse broad mite injury with herbicide injury, nutritional (boron) deficiencies or physiological disorders. With a 20x hand lens, inspect the underside of the leaves for the mites and their eggs.
Vegetable Bedding Plant Fertility Program
There are numerous factors affecting the growth of vegetable bedding plants. Two factors which have a dramatic effect on growth are the watering and fertilization programs used in the greenhouse.
Water Quality: It is advisable to have your water tested prior to the spring growing season. Your greenhouse fertilizer program should be adjusted according to test results.
Watering: The amount of water and frequency of watering will vary depending on container size, growing media, greenhouse ventilation and weather conditions. It is important to water thoroughly, to moisten the entire container, which will promote root growth to the bottom of the container. If this is not done, root growth will develop in the upper part of the container and plants with be more prone to drying and drought stress. Allow plants to dry down before watering, but do not let the plant wilt severely, as this will damage roots. Vegetable bedding plants should be watered thoroughly early enough in the day to allow foliage to dry before evening. If foliage remains wet overnight, foliar disease problems will occur.
Choosing Fertilizers: Factors to be considered when choosing fertilizers include, the ratio of ammonium to nitrate-N, trace element charge, content of calcium and magnesium, and potential acidity or basicity. Commonly used fertilizers include 15-0-15 Dark Weather Feed, 15-15-15, 15-16-17 and 20-10 20 or Cal-Mag 15-5-15.
Peat-Lite Specials (15-16-17, 20-10-20). Currently these fertilizers are among the most popular for routine fertilization of bedding plants. Both are high (>50%) nitrate fertilizers. However, these fertilizers also have elevated trace element levels which may raise Fe and Mn to toxic levels at low pH. Both are acid-forming fertilizers, but 20-10-20 has the higher potential acidity.
15-15-15 Geranium Special. "Triple 15" is a good alternative to the Peat-Lite Specials for crops sensitive to trace element toxicities. Trace element levels supplied by this fertilizer are lower than the Peat-lite Specials. Otherwise, at the same rate of N, plant response will be very similar to 15-16-17. This is an acid-forming fertilizer also; the potential acidity is slightly higher than 15-16-17.
20-20-20 General Purpose. Growers who use this fertilizer on soilless media risk ammonium toxicity because the N in this fertilizer is 75% ammonium and urea. Some growers who use media containing soil do not appear to have problems. If 20-20-20 is used, the growing medium should be tested frequently for ammonium. 20-20-20 supplies trace elements and has the highest potential acidity of fertilizers commonly used in New England greenhouses. Note that tomato, eggplant and pepper plants are especially sensitive to ammonium.
Low Phosphorus Fertilizers (20-0-20, 20-1-20, 15-0-15). These fertilizers can be tried as an alternative to chemical growth regulators for vegetable bedding plants. This technique of growth control is sometimes called "phosphorus starvation." It is generally believed that more P than necessary is being applied to greenhouse crops. Too much P may cause plants to stretch and P is a pollutant. Unfortunately, in terms of height control, these fertilizers may be of no benefit if they are applied to a growth medium containing super phosphate or a high starter charge of P. Also, there is a risk of P deficiency if the fertilizers are used continuously with low P growth media. The low P fertilizers are quite different in many ways. 15-0-15 and 20-0-20 supply Ca. 15-0-15 is a basic (raises pH) fertilizer containing about 95% nitrate and 20-0-20 is a neutral fertilizer and is 50% nitrate. 20-1-20 is an acidic fertilizer and it does not supply Ca, but it is about 70% nitrate.
Calcium nitrate and potassium nitrate (15-0-15). Use of this fertilizer combination greatly reduces the chance of trace element toxicities. Some growers alternate its use with the Peat-Lite Specials on a 2-3 week basis to supply Ca and to counter the acidic effect of the Peat-Lites. However, both super phosphate and a trace element fertilizer must be incorporated in the growing medium if this combination is to be used as the sole fertilizer.
Nitrogen, Phosphorus, Potassium
Nitrogen. Nitrogen concentration in the greenhouse fertilizer program has a greater affect on the growth of transplants in the greenhouse than the other two major nutrients. Increasing the level of nitrogen results in taller transplants with thicker stem diameters and heavier plant weights. Applying too much nitrogen in the greenhouse results in soft, poor quality transplants. These lush transplants may also be more prone to phloem feeding insects such as aphids.
Phosphorus: Phosphorus has a limited affect on the growth of bedding plants when compared to nitrogen, but should be included as part of a complete fertilizer. Increasing the phosphorus concentration results in a moderate increase in transplant height, stem diameter, and shoot fresh and dry weight. If phosphorus is restricted to the point at which the plants show extreme phosphorus deficiency (purple leaves and stems, stunted plants), field performance will be reduced.
Potassium: Potassium has the least affect on the growth of plug tomato transplants of the three major nutrients. Adequate potassium is applied as part of a complete fertilizer.
Fertilizer Solution Volume: The volume of fertilizer solution applied has a dramatic affect on the growth of the vegetable bedding plants. As the volume of water-soluble fertilizer increases, the quantity of nutrients delivered to the plant also increases resulting in an increase in height, stem diameter and plant weight. Doubling the volume applied also doubles the amount of each nutrient potentially available to the plant.
Plant growth rate and environmental conditions. In general, nutrient requirements of vegetable bedding plants are greatest during periods of rapid growth. Too much fertilizer during slow growth periods may lead to excess soluble salts; failure to provide enough fertilizer during periods of rapid growth will lead to deficiency.
General fertilizer guidelines
Have your soil tested each month to adjust your fertilizer program and to prevent problems.
Optimum pH range for vegetable bedding plants: 5.5 to 6.5
While plants are in the plug or seedling stage, use a complete water soluble fertilizer at the rate of 50 – 100 ppm N every time plants are watered and use clear water (no fertilizer) every third watering. Use the lower rate (50 ppm) early and the higher rate (100 ppm) later if the seedlings are to be held in the flat or tray three or more weeks before transplanting. Shortly after transplanting, as plants approach rapid growth, increase the rate to 200 ppm N at every watering or 300 ppm N once every 7 days, watering with clear water 2 or 3 times in-between each fertilization. Small, slow-growing plants should receive lower rates or less frequent application until they are well-established. Care should be taken not to over-fertilize vegetable bedding plants because no growth regulators are labeled for use on edible crops.
Vegetable bedding plants are subject to the same nutrient disorders as other plants. Early in production serious problems are: high soluble salts, trace element toxicities, and ammonium toxicity. Late in production, particularly in cell packs, plants may develop nitrogen deficiency symptoms as the earliest indication of insufficient fertility.
Soluble Salts. Injury to bedding plants from excess salts seems to be most common shortly after transplanting. Seedlings are much less tolerant than established, rapidly growing plants. Some soilless mixes may contain enough "starter charge" to cause excess salts problems in the first few weeks after transplanting, particularly when a water-soluble fertilizer is also applied. Excessive drying, poor drainage, and uneven watering are factors which can aggravate this problem. Check roots of plants often and conduct regular soil tests to identify and prevent problems. It is difficult to diagnose a soluble salts problem by symptoms alone. Often nutrient deficiencies and root diseases cause the same symptoms. Therefore, a soil test is advisable. Check with your Soil Testing Laboratory or Extension Specialist as to appropriate EC levels.
Trace element toxicities. Iron (Fe) and/or manganese (Mn) can be accumulated to toxic levels by tomato plants. Symptoms appear as numerous small dark spots and mottling of the foliage. The potential sources of excess Fe and Mn are: trace element fertilizers in the mix, water-soluble fertilizers with elevated trace elements levels, and sometimes irrigation water. Low growth medium pH aggravates the problem by increasing Fe and Mn availability. Toxicity can be avoided by keeping the pH in the range of 5.8 – 6.0 for susceptible crops and by the use of fertilizers with lower trace element levels.
Ammonium toxicity. This is less common today because most growers use water-soluble fertilizers that supply about 50/50 ammonium and nitrate to fertilize plants in soilless media. Tomato, eggplant, and pepper are most sensitive to ammonium nitrogen, but many other bedding plants can be harmed if ammonium becomes excessive. Too much ammonium during the early spring (February or March) in low light and cool media conditions can be toxic to plants.
Organic Vegetable Bedding Plant Fertility
The quality of the planting mix is important to insure proper plant health in organic production. Conventional growing media that contains synthetic ingredients cannot be used in organic production of field transplants, container plants, and greenhouse crops. However, acceptable growing media can be composed from a wide variety of approved materials. These organic blends may be purchased off-the-shelf, custom-blended by manufacturers, or produced on-the-farm.
Most commercial potting mixes contain synthetic fertilizers and wetting agents that do not meet organic standards. One alternative is to arrange a special order from a commercial supplier who agrees to exclude starter fertilizers and wetting agents and then, plan to add your own. Purchasing a commercially prepared organic mix is the easiest way to get started and most growers choose this option to reduce the risk of soil-borne diseases. Common components such as peat moss, perlite, vermiculite, and coconut coir are acceptable for organic certification. Compost, being the most renewable, is a preferred material for many organic grower
Dr. John Biernbaum, from Michigan State University, for his research, chooses a 50/50 mixture of peat and compost with a pH of 6.0 as an organic potting media. He makes his own compost from garden waste, straw, hay and sheep/horse manure and screens the compost to provide a uniform product. This is just one of many options; however the finished compost product needs to have good physical, chemical and biological properties.There are also many fertility management options such as supplementing with liquid organic fertilizers or using a growing media that contains sufficient amounts of major nutrients to grow the transplants while they are in the greenhouse. In his studies, Dr. Biernham, used liquid fish emulsion (5-1-1) as a sole fertilizer with a soilless peat based medium and coconut coir successfully for several months. No synthetic fertilizer was used.
Fish emulsion fertilizers are likely to have an odor and fertilizing less often may be preferred, for example, every two weeks or once a month. The rate applied will vary depending upon how often one fertilizes.Plants fertilized with organic fertilizers will not show the rapid growth response seen with synthetic fertilizers. With this method, John suggests beginning with a growing media containing 60-70% peat and 30-40% perlite and/or vermiculite without fertilizer and wetting agent, but limed to a pH of 5.5 to 6.5. Apply the water soluble organic fertilizer as needed, usually soon after seed emergence or at transplanting.
Another option recommended by Eliot Coleman, from Four Season Farm, Maine is to use a blend of peat and compost or peat-based soilless medium and compost mixed with 14 lbs. per cubic yard of equal parts blood meal or alfalfa meal for nitrogen, rock phosphate for phosphorus and green sand or organic approved potassium sulfate for potassium. He lets the blend sit for a month or more before use.
A third option is to use mature, well-balanced compost blended with peat and possibly perlite and/or vermiculite for aeration to supply all the nutrients to grow and finish transplants. Nutrient sources such as alfalfa, alfalfa meal and other organic approved components can be incorporated during the composting process. Compost will mature during the fall and can be stored for use until spring. These last two options add some nutrients to the root medium, so plant nutrition is not dependent on liquid fertilizer. However, these options require purchasing the organic nutrient sources and making sure the rate and method of application are correct.For more information see:
Biernbaum, John. 2006. MSU Organic Greenhouse
Transplants; Illinois Organic Conference.
ATTRA - National
Sustainable Agriculture Information Service
Leanne Pundt, Extension Educator, University of Connecticut, Cooperative Extension System Extension
Tina Smith, Extension Educator Floriculture Program, Department of Plant and Soil Sciences, University of Massachusetts
Information on our site was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate.
The information in this material is for educational purposes. The recommendations contained are based on the best available knowledge at the time of printing. Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension system does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available.All agrochemicals/pesticides listed are registered for suggested uses in accordance with federal and Connecticut state laws and regulations as of the date of printing. If the information does not agree with current labeling, follow the label instructions. The label is the law.Warning! Agrochemicals/pesticides are dangerous. Read and follow all instructions and safety precautions on labels. Carefully handle and store agrochemicals/pesticides in originally labeled containers immediately in a safe manner and place. Contact the Connecticut Department of Environmental Protection for current regulations.The user of this information assumes all risks for personal injury or property damage.Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Kirklyn M. Kerr, Director, Cooperative Extension System, The University of Connecticut, Storrs. The Connecticut Cooperative Extension System offers its programs to persons regardless of race, color, national origin, sex, age or disability and is an equal opportunity employer.