Transplant Insect and Mite Management

Monitoring

A regular monitoring program is the basis of pest management. Conduct regular, weekly scouting to detect problems early. 

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

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, pepper, eggplant and leafy greens 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 and eggplant will also indicate an early thrips population. Look for distorted, young leaves with silvery flecked scars, signs of thrips feeding damage.

Recordkeeping 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 recordkeeping 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?  Do you need to release more natural enemies? Are insects migrating from weeds under the benches to your crops? Is the treatment from last week working? See Table 20 and Table 21 for selected materials labeled for managing diseases and insects and mites on greenhouse-grown vegetable transplants. Follow label instructions before using the material on vegetable transplants. The product must be used only for crops for which the compound is registered.

Biological Control for Insects and Mites

Biological control is the use of living organisms (biological control agents) such as insects, predatory mites, fungi or bacteria to manage pests.  They are best used preventively, early in the cropping cycle. Growers often start with the use of insect killing nematodes against fungus gnat larvae,  different predatory mite species for use against thrips and spider mites and host specific parastic wasps against whiteflies. 

Some of the advantages of using biological control agents include:

  • less worker exposure to pesticide residues. 
  • less chance of plant damage from sprays. 
  • improved plant quality.
  • no re-entry intervals (REI) to follow. 

Biological control programs use living organisms, so extra care and effort is needed to make these programs work. Committment, patience, and a desire to learn about the life history and environmental requirements of the pest and it's natural enemy are all needed.  The support of the owner, management and a dedicated staff are all needed. 

A detailed plan of action is needed to ensure success. Biological controls are best used with proper cultural controls and sanitation practices. Start planning 6 months to one year in advance. Develop a spreadsheet of your planting schedule and when your greenhouses will be open for production to help pre-order biological control agents.  Accurately identify the key pests in your production system. Natural enemies, especially parasites, are often very specific to a particular pest. They may also be shipped in a stage that does not attack the targeted pest.  Many insecticide residues can adversely affect natural enemies for up to 3 to 4 months after their application.  Review your pesticide use before starting biological controls.  For more information on the compatibility of pest control materials with natural enemies, refer to online resources, such as:

  1. Koppert's online interactive database: www.koppert.com and see side effects database under popular links 
  2. Biobest: http://www.biobestgroup.com/ (download side effects APP) 
  3. BASF Nemasys Beneficial Nematodes Chemical Compatibility Guide:https://betterplants.basf.us/content/dam/cxm/agriculture/better-plants/united-states/english/products/nemasys-beneficial-nematodes/nemasys-chemical-compatibility-guide.pdf
  4. Bioline Agrosciences and download Bioline APP 

Start in a small trial area to become familiar with releasing, monitoring and evaluating the effectiveness of natural enemies. 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. Vegetable transplants with only one or two key insect pests or with a longer production schedule may be logical candidates for biological control.  Some growers have started with using biological controls against fungus gnats (beneficial nematodes) and thrips (predatory mites), especially if long term crops are in the same greenhouse. Be sure that natural enemies are received from your supplier quickly (within 4 days), and that they are kept cool during shipment.  The predatory mites, Phytoseiulus persimilis that are used against two spotted spider mites, that are often shipped without a food source, should be received after an overnight delivery. 

Inspect natural enemies for viability and quality when they are received. Biological control suppliers often send a description of what to look for when receiving the natural enemies.  The package containing biological control agents should be shipped in a sturdy container, such as a polystyrene box that minimizes exposure to high and low temperatures.  When you receive the natural enemies, check the temperature within the shipping box with an infrared thermometer. A moldy odor or condensation is of concern.  Most natural enemies should be released immediately upon arrival.  For more specific information, see Grower Guide: Quality Assurance of Biocontrol Products compiled by Dr. R. Buitenhuis.

In order for a biological control program to be successful, it is critical to establish a good working relationship with your supplier or distributor of biological control agents.  Ask them if they provide technicial support or consulting services and what their delivery schedule and shipping costs will be.   Here is a partial list of some of the biological control suppliers or distributors of biological control agents used by New England greenhouse growers. 

See Table 18 for information on scouting for key pests and biological control options and Table 21 for insecticides labeled for vegetable transplants.

Alyssum, "Lobularia maritima", attracts syrphid flies, lacewings, and parasitic wasps and provides sugars needed by parasitic wasps (Encarsia) to fly. These plantings can help attract and sustain natural enemies.

Aphids

Lifecycle: Several species of aphids can occur on vegetable transplants, but the most common are green peach, melon, foxglove and potato. Aphids are small, 1/16" 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 or "tailpipes" (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 cornicles. The legs and antennae also have black markings. Foxglove aphids cause more leaf distortion than green peach or melon aphids. Potato aphids have antennae longer than their bodies with long cylindrical tailpipes and are green or pink.

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 7-10 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 and their white shed cast skins may be unsightly. Sometimes, these white cast skins are mistakenly identified as whiteflies. Honeydew can cover leaves and provide a food source for a superficial black fungus known as "sooty mold." Aphids are present on weeds and winged aphids may also enter the greenhouse through vents. Aphids can also transmit certain viruses.

Monitoring: Examine the foliage, along stems and new growth of key plants such as pepper, eggplant, 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.

Caterpillars

Lifecycle: Caterpillars are the immature or larval stage of moths and butterflies (Lepidoptera).  Most overwinter outdoors and may migrate into greenhouses especially during the summer and fall.  Although they are not major pests of greenhouse crops, night flying moths may be attracted to lights near greenhouses.  Female moths enter the greenhouse to lay their eggs on susceptible crops. Their life cycle consists of egg, larvae, pupa and adult.   Females emit pheromones that attract males, and after mating, the females lay eggs that hatch into rapidly growing caterpillars. They may molt up to 3-5 times before entering a resting stage.  Day flying butterflies, such as the imported cabbageworm, develop into a chrysalis as a resting stage and night flying moths develop into a pupal cocoon. Depending upon the species there may be from 1 to 3 or 4 generations a year.  Cole crops are especially susceptible to damage from the imported cabbageworm, cabbage looper, diamondback moth and cross-striped cabbageworm.

Monitoring: Visually inspect plants when adults are active. In greenhouses, pay close attention to plants near doors, vents and other openings, especially near weedy areas or near vegetable fields.

Fungus Gnats, Shore Flies, and Predatory or Beneficial Hunter Flies

Lifecycle: The damp, moist environment in greenhouses favors both fungus gnats and shore flies. Fungus gnat larvae are translucent, white and legless, about 1/4" long when mature, and have a shiny black head. The mosquito-like adult is about 1/8" 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 potting 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 12-14 days before changing into pupae. The pupal stage may last 5-6 days. Adults live up to ten days. The life cycle from egg to adult requires approximately 21-28 days depending on greenhouse temperatures.

Adult shore flies also occur in damp greenhouses. Shore flies are often misidentified as fungus gnats or hunter flies but they have a distinctly different appearance. The adult shore fly is about 1/8" long and has a robust body, very short antennae, shorter legs and dark wings with about five light spots. Adults may be seen resting on plant leaves. Larvae are off-white and do not have distinct head capsules that are characteristic of fungus gnat larvae. 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.

Adult hunter flies, a natural enemy (beneficial fly) are also found on sticky cards that may be mistaken for shore flies. Hunter flies can be distinguished from shore flies, by their size and color. Hunter flies are about twice as large as shore flies with wings that are uniformly clear and do not have light spots on their wings. Hunter flies are in the same family as common houseflies and are similar in appearance. Hunter flies may prey upon fungus gnats and shore flies.

Monitoring: To monitor for fungus gnat larvae, place raw potato chunks (with peel removed) on the soil surface. Larvae are attracted to the potato chunks and will congregate underneath. Check the potato chunks after 2 days for the larvae. Potato disks cut one inch in diameter and 0.5"-1" thick are effective. 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 fungus gnats can be monitored with yellow sticky cards placed at the base of the plant at the 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.

Leafminers

Spinach leafminer (Pegomya hyoscyami Panzer) and beet leafminer (Pegomya betae) feed between the upper and lower epidermis of the leaf. Early damage is a slender, winding ‘mine’ or tunnel, but as the larva feeds and grows these may expand and become blotches on the leaves.  Spinach and beet leafminers may cause damage on chard, beet, and spinach transplants.

Life Cycle: Adult spinach and beet leafminers are flies that overwinter as pupae in the soil and emerge in late-April and May. The two species are similar in behavior, appearance, plant hosts, and damage, but beet leafminer adults are slightly larger and darker, and beet leafminers prefer laying eggs on beet leaves. The small, gray adult flies lay small, oblong white eggs in clusters on the undersides of leaves. Eggs develop into pale, white maggots that damage the leaves. The larva burrows between the upper and lower epidermis of the leaf and feeds, creating a slender, winding ‘mine’ or tunnel. This expands into large blotches of translucent, dead tissue across the leaf, with a white maggot inside.  When fully grown, maggots usually drop into the soil to pupate, though they may also pupate inside the leaf. The entire life cycle is 30-40 days and there are three to four generations per season.

Monitoring: Look for the small, oblong, white eggs that are laid in neat clusters on the underside of the leaves.  Inside the mines look for one or several pale, white maggots.

Mites

Two-spotted Spider Mites

Lifecycle: Two-spotted spider mites can be found on vegetable transplants. Adult females are approximately 1/50" 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 3-4 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 (80oF and 30-50% RH) favor spider mite development.

Monitoring: Check for mites by examining foliage. Adult spider mites are not found on sticky cards. Mites often develop as localized infestations on bean, tomato, or eggplant. Sample plants by turning over leaves and with a hands-free magnifier (Optivisor™) or hand lens, check for the presence of spider mites.

Broad 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 (70-80o F and 80%-90% RH). 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, salvia, ivy, verbena and zinnia. They may migrate to pepper or tomato. Look for characteristic damage including leaf edges curling downward. Terminal buds may be killed. As they feed, broad mites inject toxic saliva, which results in the characteristic twisted, distorted growth. Broad mite injury can be mistaken for herbicide injury, nutritional (boron or calcium) deficiencies or physiological disorders. Inspect the underside of the leaves for the mites and their eggs with a 20x hand lens or submit samples to a laboratory for diagnosis. Microscopic examination is often needed.

Cyclamen Mites

Life Cycle: The shiny, orange-tinted cyclamen mites prefer to hide in buds or deep within the flowers. Eggs are deposited in moist places at the base of the plant. Cyclamen mites can complete their life cycle in 1-3 weeks. Females can live up to one month and can reproduce without mating. Cyclamen mite females lay 2-3 eggs per day for up to 2-3 weeks. Cyclamen mite eggs are oval, smooth and about one half the size of the adult female. Larvae hatch from the eggs in 3-7 days. The slow moving white larvae feed for 4-7 days. Cyclamen mites prefer high relative humidity (80%-90% RH) and temperatures of 60ºF. Cyclamen mites affect a number of ornamental bedding plants including dahlia, fuchsia, gerbera daisy, petunias and viola. 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 1/100th of an inch long. Examination under a microscope is often needed to confirm the presence of cyclamen mites.

Slugs

Life Cycle: Slugs are classified as mollusks and are covered with mucous-like slime that protects their bodies from desiccation. Slugs lay translucent pearl-shaped eggs in clusters of 20-100 in cool, moist locations such as in the soil or growing medium or underneath containers. Eggs hatch in less than 10 days at 50ºF. Young slugs resemble adults but are lighter in color and smaller. They mature in 3-12 months and adults may live a year or more. Slugs contain both male and female organs and may alternate sexes at different times during adulthood.

Monitoring: Slugs vary in size from 3/4 to 1-1/2" in length. Their color ranges from pale yellow to lavender or purple. Slugs feed on a wide-range of greenhouse grown crops at night. They use their chewing mouthparts to create holes in leaves and stems. Feeding damage from slugs may be confused with that of caterpillars. However, slugs completely consume leaves and stems, whereas caterpillars may leave portions of stems or leaf veins. Slugs also leave shiny mucous-like slime trails.

Thrips

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" long, with narrow bodies and fringed wings. Females are reddish brown and males are light tan to yellow. The wingless immature larval 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 fall off the leaves and drop into the growing media, passing through two stages, after which adults emerge. The egg to adult lifecycle can be completed in 2-4 weeks 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 spray coverage when plant canopies are small. Symptoms of their feeding are often not noticed until the damage has occurred. Eggplant, tomato, pepper and leafy greens are prone to thrips infestations. Yellow sticky cards, key plants and indicator plants can be used 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 their movement. The light to medium-blue sticky cards may catch more thrips (and shore flies) 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. See Key plants and indicator plants earlier in this section for more monitoring information.

Whiteflies

Lifecycle: The sweet potato (a.k.a. silverleaf) whitefly B biotype (Bemisia argentifolii) and greenhouse whitefly (Trialeurodes vaporariorum) may infest vegetable transplants. However, greenhouse whitefly is the most common species in New England. Both adult and immature whiteflies have piercing sucking mouthparts to remove fluids. Like aphids, they also produce honeydew that results in sooty mold fungus. Winged adult whiteflies are 1/16" in length, and are usually found on the youngest, most tender leaves. Females may lay from 150-300 eggs, which hatch into first-instar nymphs in about a week. These “crawlers” move for a short distance before settling down to feed. After three molts, a pupal stage is formed, and adults emerge in about six days. Whiteflies complete their egg to adult cycle in 21-36 days, depending upon greenhouse temperatures.

Monitoring: To monitor whiteflies, check susceptible plants, such as tomato, 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.

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