Fungus gnats and shore flies, two-spotted spider mites, broad mites, cyclamen mites, mealybugs, aphids, whiteflies and western flower thrips can all be challenging to manage during the busy spring bedding plant season. This fact sheet reviews how to monitor for these common pests, provides information on their biology and life cycle as well as some tips on management.
Symptoms: Fungus gnat larvae feed on young roots causing stunting or death in severe cases. They feed on callus tissue delaying the rooting of cuttings. Fungus gnats also help spread fungal diseases such as Pythium, Thielaviopsis, Fusarium and Botrytis.
Monitoring: Place yellow sticky cards just above soil or media surface to detect winged adults. Use potato chunks (1/4 of a potato) to detect young larvae. For plugs, cut potatoes to resemble a "french fry" and place in the small containers. Check every two days. Look for small, white larvae (1/4 of an inch long when fully grown) with black head on the surface of the potato and growing media. Inspect incoming plants for larvae or their feeding damage.
Biology and Life Cycle: Fungus gnats develop from egg, larval, pupal and adult. Overlapping generations frequently occur in the greenhouse. At 72o F, they may complete their life cycle in about 3 to 4 weeks. Females can lay up to150 eggs.
Cultural Controls: Don't overwater plants and keep the top 3 inches of soil drier. Keep greenhouse floors free of puddles, debris, weeds, and spilled media.
Biological Control: Soil drenches of Gnatrol (Bacillus thuriengenis ssp. israelensis), can be used against the 1st instar larvae. Repeated applications (two or more) may be needed at the highest rate listed on the label to target this susceptible life stage. Beneficial nematodes (Steinermena feltiae) (Scanmask, Nemasys or Entonem) can also applied to areas where fungus gnats breed. Hypoaspis miles is a small (1/25 of an inch and smaller), brown predatory mite that feeds upon fungus gnat larvae. Adults and larvae of the rove beetle (Atheta coriaria) are predaceous on fungus gnat larvae, eggs and pupae.
Chemical Control: Treatments should be directed against the early instar larvae. Many insect growth regulators including Distance, Citation, Adept and Azatin, Ornazin or Aza-Direct have performed well against fungus gnat larvae in recent university trials. Only Azatin, Ornazin & Aza-Direct and Gnatrol are labeled for fully drenching pots (as opposed to a surface treatment). The neonictotindoids Safari (dinotefuran) (soon to be registered in CT), Flagship (thiamethoxam), and imidacloprid (Marathon) are also labeled as a drench for use against fungus gnat larvae.
If high populations are present, you may also consider treating for the adults. Pyrethroids such as Orthene TR, Attain TR, Talstar F, Decathlon, Tame/Orthene TR, Ultra Fine oil, Synergy Super Fine Spray Oil Emulsion, Astro, Pyrenone Crop Spray, 1100 Pyrethrum TR, or Pyrethrum TR are labeled for use against adults.
Symptoms: Fecal spots may be seen on the leaves (larger than the fecal spots from thrips). Adult shore flies (< 1/8 of an inch long) may help spread diseases and are also a nuisance. The small, white larvae (with no distinctive head capsule) feed on algae, not crop plants.
Monitoring: Place yellow sticky cards in the greenhouse, especially in propagation areas. Larvae and adults are often found near algae.
Biology and Life Cycle: Adult shore flies lay oblong, white eggs (up to 300) on algal scum or in very wet areas with decomposing organic matter. Eggs hatch into maggots with two forked, dark tipped breathing tubes at their rear. Maggots develop into dark brown pupae that are also found in the algae. Shore flies develop from egg to adult in about 9 to 11 days. Adults often live for 2 to 3 weeks.
Cultural Control: Manage algae. Don't overwater plants. Avoid fertilizer runoff. Practice good sanitation. Yellow sticky tape can be used to trap out the adults.
Biological Control: The rove beetle (Atheta coriaria) is a predator of shore fly and fungus gnat larvae and pupating thrips. It may be able to colonize areas under greenhouse benches where there are fewer sprays. Nematodes and predatory mites used for fungus gnat control do not appear to work well against shore flies because of the semi-aquatic environment in which they live.
Chemical Control: Horticultural oil and insecticidal soaps can by used against the adults. Treat in the morning or late in the day when adults are settled and you are more likely to make contact with them.
Key bedding plants affected: Ageratum, buddleia, brugmansia, dracaena (spike), ivy geraniums, many different herbs (i.e. lemon balm, sage, and lemon verbena, lemon grass), fuchsia, thunbergia, lantana, hibiscus, hollyhock, hydrangea, marigolds, New Guinea impatiens, roses, salvia, sweet potato vine, viola, verbena, etc.
Symptoms: As mites feed, they pierce cells, and a chlorotic spot develops. Fine flecking or stippling occurs as chlorophyll is removed from the leaves. Leaves can turn yellow, become bronzed and drop from the plant. During outbreaks, fine webbing can be seen.
Monitoring: Look for stippling and flecking. Turn over leaves, especially the older, more mature leaves, and look along the leaf veins for the mites. As mites feed upon ivy geraniums, leaves develop edema-like symptoms.
Two-spotted mites are small, (1/50 of an inch long), oval-shaped and yellow-orange to green in color. They prefer warm, dry areas with low humidity. Mites may be found in areas near furnaces, the south or west side of greenhouses or on hanging baskets in the upper canopy. Look for eggs, mites, shed skins, and droppings with a 10x to 20x hand lens. Two-spotted spider mites may go into diapause during several months in the winter.
Lima beans or radishes can be used as indicator plants to detect mites before damage occurs on the crop.
Biology and Life Cycle: Two-spotted spider mites develop from egg, larvae, nymph and adult. Females can lay up to 120 eggs. Development takes from 7 days at 81o F to about 20 days at 64o F.
Cultural Control: Remove weeds or any pet plants that may harbor mites. Do not over-fertilize plants. Avoid placing mite-prone species in hot, dry locations in your greenhouse. Mites may be spread on workers clothing or tools. Work in and scout mite infested areas last. Some cultivars of New Guinea impatiens have been reported to be resistant.
Biological Control: A number of species of predatory mites are commercially available. Phytosieulus persimilis performs best under humid conditions and moderate temperatures. Neoseilus californicus persists well at low pest densities. A predatory midge, Feltiella acarisuga is commercially available. The adult can fly, so it may be useful in reaching mites found in hanging baskets. Galendromus occidentalis tolerates hot conditions as long as the relative humidity is over 50%.
Chemical Control: Broad-spectrum pesticides, especially certain pyrethroids and organophosphates, are harsh on predatory mites and may result in mite outbreaks, especially on crops grown outdoors. Certain organophosphates (i.e. Orthene) may also increase mite egg laying.
There are no systemic miticides. Coverage is especially important for the miticides that work by contact. Translaminar (move through the leaf) miticides include Avid, TetraSan and Pylon.
Two-spotted spider mites develop resistance to miticides very rapidly. The miticides used in your rotation schedule should have different modes of action (i.e come from different pesticide classes and work differently). See the most recent edition of New England Greenhouse Floriculture Guide for a chart of classes of insecticides and miticides. Some miticide rotations to avoid include: Hexygon with Ovation, Akari with Sanmite and Talstar/Mavrik/ or Tame. (These products work in the same way).
Many miticides work against specific life stages, so optimal timing and application is needed to get the desired results. Researchers have reported good control of mites with Akari, Hexygon, Ovation, Sanmite and TetraSan. Ovation and Hexygon are primarily effective against eggs and early stages of mites. They are best used early in an infestation, before there are many adult mites. TetraSan is a growth regulator that is slow acting, but effective miticide. It inhibits the molting process on mite eggs and nymphs. Akari is a contact miticide that stops the mites from feeding and laying eggs.
For quick knockdown, Avid, Floramite, Kelthane, Pylon or spray oils (Ultra-Fine Oils or Synergy Super Fine Spray Oil Emulsion ) are reported to work well. Floramite is rapidly degraded in alkaline solutions. Correct pH of spray solutions with phase 5 or another product.
Key Bedding Plants Affected: African violets, ageratum, begonia, dahlia, gerbera, gloxinia, English ivy, New Guinea impatiens, salvia, snapdragon, verbena, vegetative petunia, peppers, zinnia etc.
Symptoms: Leave edges curl downward. Flowers and buds become distorted and do not open. Terminal buds may be killed. As they feed, broad mites inject toxic saliva, which results in the characteristic twisted, distorted growth. Do not confuse broad mite injury with herbicide injury, nutritional (boron) deficiencies or physiological disorders. For example, during late winter production, with cool temperatures and high humidity, you may see some leaf curling and twisting on New Guinea impatiens, which is a physiological disorder and not broad mite injury.
Monitoring: Look for characteristic damage. With a 20x hand lens, inspect the underside of the leaves for the mites and their eggs. Often, microscopic examination is helpful.
Biology and Life Cycle: Broad mites can be distinguished from cyclamen mites by their egg stage. Eggs are covered with "bumps" that look like a row of diamonds. Adults and larvae are smaller than the cyclamen mite and walk rapidly on the underside of leaves. 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.
Solutions: Inspect incoming plants. If detected early, rogue infested plants. A number of miticides including Avid, Pylon, Sanmite, Talstar and Kelthane are labeled for use against broad mites. Translaminar miticides include Avid and Pylon. Some predatory mites will feed on broad mites, however, little research has been conducted on how to use these predators in the greenhouse.
Key bedding plants affected: Aconite, African violet, begonia, chrysanthemum, dahlia, delphinium, exacum, fuchsia, gerbera, rosemary, petunia, impatiens, English ivy, geranium, garden mums, kalanchoe, lamium, loosestrife, snapdragon, strawberry, verbena, and viola.
Symptoms: Mites pierce tissue with their mouthparts and suck out cell contents. Damage may be concentrated near the buds or occur on the entire plant. Symptoms include inward curling of the leaves, puckering and crinkling. Pitlike depressions may develop. Flower buds may not open.
Monitoring: Look for signs of damage. The mite is only 1/100 of an inch long. Examination under a microscope is often needed.
Biology and Life Cycle: The shiny, orange-tinted cylamen 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. They prefer high relative humidity and temperatures of 60o F.
Cultural Control: If only a few plants are infected, toss infected plants. Or submerge in hot water (115o F) for 15 minutes. (Certain plants may be damaged by this treatment, so test first). Prevention and sanitation are critical. Mites can easily spread on workers hands and clothing.
Biological Control: The release of the predatory mites, Neosiulus cucumeris and Amblyseius fallacis has provided the control of cyclamen mite in some crops. More research is needed for greenhouse crops.
Chemical Control: It is difficult to contact the mites deep within the buds and flowers. Repeated applications are often needed. Avid, Pylon, and Kelthane are labeled for use against cyclamen mites.
Key bedding plants affected: Cacti, coleus, croton, dracaena, English ivy, fuchsia, gardenia, hibiscus, mandevilla, orchids¸ succulents, stephanotis, etc.
Symptoms: As sap is removed from infected plants, leaves turn yellow and drop. New growth may become distorted. Honeydew can support the growth of black sooty mold fungus.
Monitoring: Look for white flecks or cottony residues along leaf midribs, on leaf or stem axils and on the underside of leaves. Adult females may crawl off plants and be found in brick crevices and under benches where they lay eggs. Honeydew, sooty mold and the presence of ants may also be an indication of mealybug infestation.
Biology and Life Cycle: Mealybugs are soft-bodied insects, from 1/8 to1/4 of an inch long, that are covered with white, waxy secretions. Their life cycle consists of an egg stage (except for the long- tailed mealybug and other species that gives birth to live young), immature stages (crawlers) and adult. The immature crawlers mature in about 6 weeks to 2 months. Mature females die after egg laying. Continuous and overlapping generations can make control difficult.
Cultural Control: Inspect incoming plants. Start with clean plant material. Do not carry over "pet plants" or stock plants that may be infested with mealybugs. Toss isolated infected plants.
Biological Control: The mealybug destroyer, (Cryptolaemus montrouzieri), is used against the citrus mealybug, but is relatively ineffective against species like the long-tailed mealybug that give birth to live young. Parasitoids may be able to suppress certain species of mealybugs in conservatories and other areas where plants are maintained for long periods of time. Botanigard may be able to suppress mealybugs.
Chemical Control: Chemical control is difficult because the mealybug's waxy covering reduces its contact with spray materials. Crawlers, with the least wax, are most susceptible to chemical treatments. Safari is very water soluble and effective against mealybugs and scale insects. Tristar and Marathon may also be effective against some species of mealybugs. Some herb growers have reported good results using insecticidal soaps (to dissolve some of the mealybug's waxy coating) followed by horticultural oil.
Green Peach Aphid
photo: Whitney Cranshaw,
Colorado State University
photo: Mississippi State University Archives, Mississippi State University
photo: University of California Cooperative Extension Central Coast Vegetable IPM Project
Symptoms: As aphids feed, new growth may become distorted. High populations can also stunt growth. Foxglove aphid causes foliar distortion that is often confused with thrips feeding damage. Some aphids may also transmit viruses.
Monitoring: Rely on random plant inspection. Yellow sticky cards will only attract winged adults moving into the greenhouse. If you see winged aphids in a closed greenhouse in the winter, look for an aphid infestation on crops or weeds.
Look for signs of aphid activity: shed skins, honeydew and sooty mold. Infestations are often localized. Inspect on young growing tips and underside of leaves for the pear-shaped aphids about 1/8 of an inch long with "tailpipes" (cornicles) protruding from the rear of their abdomen. Green peach aphid is green with "tailpipes" the same color as their body. Melon aphids are smaller, light yellow or dark green to black with dark, black "tailpipes". Foxglove aphids are slightly longer than green peach aphids with dark joints on their legs and antennae.
Biology and Life Cycle: In the greenhouse, all aphids are females that give birth to young aphids (nymphs). There is no egg stage. Nymphs can begin to reproduce in as little as 7 to 10 days. High fecundity and quick maturation can lead to populations appearing to explode overnight.
Cultural Control: Avoid high nitrogen fertilization that promotes lush growth favorable to aphids. Remove weeds and pet plants that can be sources of aphid infestations. Inspect incoming plants for signs of aphids.
Biological Control: Beauvaria bassiana (Botanigard) may be an option when populations are low, plants are small and good coverage can be achieved. Repeated applications with a fine mist spray are needed.
Outdoors, a complex of natural enemies are present that can help keep aphid populations in check. These include ladybird beetles, lacewings, flower flies, predaceous midges, and parasitic wasps.
Preventative releases of aphid parasites can be used in bedding plant production. For green peach aphid, release Aphidius colemani. For foxglove aphid, release Aphidius ervi or Aphelinus abdominalis. Researchers are also investigating the use of "banker plants" to help growers reduce costs of biological control. For example, Aphidius may maintained on "banker plants" hosting cereal aphids that are not typically a pest of bedding plants.
Chemical Control. Systemic insecticides such as Tristar, Flagship (spray), Safari (drench) and Marathon seem to be performing well. Many growers also report good results with Endeavor. Ultra Fine Oil or Synergy Super Fine Spray Oil can also be used. Thorough coverage is needed when using contact material such as oils or soaps. When using wet sprays, repeated applications every 5 to 7 days are often needed.
Key bedding plants affected: Ageratum, alyssum, zonal geranium (Aurora and Snow Mass), fuchsia, gerbera daisies, herbs, hydrangea, lantana, primula, salvia, tomato, zinnia, etc.
Symptoms: The mere presence of adult whiteflies may be objectionable to customers. Heavy populations can stunt plants and reduce their vigor. Honeydew and sooty mold can then develop.
Monitoring: Use yellow sticky cards to attract adults. Rely on random plant inspections for the adults, which can be found on the young tender growth and immature scale-like whiteflies found on underside of leaves.
Biology and Life Cycle: Whiteflies develop from egg, scale-like crawlers, pupae to adult. Females can lay up to 200 eggs (depending upon host plant and temperature). At 72o F, greenhouse whiteflies can complete their life cycle in about 32 days.
Cultural Control: Avoid keeping poinsettias or "pet plants" in the greenhouse during bedding plant season. Remove weeds. Inspect incoming plants for presence of whiteflies.
Biological Control: Parasitic wasps (Eretmocerus californicus) are commercially available. If whitefly numbers are high, first use an insect growth regulator that is compatible with Eretmocerus to reduce numbers and then release this parasitic wasp.
Chemical Control: Spray coverage and timing is critical to target the most susceptible life stage. Whitefly eggs and pupae are tolerant to many insecticides.
Insect growth regulators including Endeavor, Distance or Enstar may be used against whitefly nymphs. The systemic materials Tristar, Flagship or Safari may also be applied. Repeated applications of Botanigard may be an option, provided you can obtain good coverage. Horticultural oil can also be used as a foliar spray. Spot test first on a small scale to avoid phytotoxicity and apply during conditions that promote rapid drying.
Key Bedding Plants Affected: Ageratum, alyssum, basil, begonia, dahlia, New Guinea Impatiens, petunia, pepper, portulaca, primula, snapdragon, tomato, verbena, zinnia and many others.
Symptoms: As thrips feed, flowers and foliage becomes distorted or stunted. You can also see white scarring on the foliage and flowers as well as small black dots (frass). The western flower thrips also vector tospoviruses including INSV (impatiens necrotic spot virus) and TSWV (tomato spotted wilt virus).
Monitoring: Place sticky cards just above foliage to detect winged adults,
To best determine placement, place twice the recommended number of cards, in order to determine "hot spots" in your greenhouse. Early in the season, place cards at floor level to detect any thrips overwintering in dirt floors. Sticky card counts may peak every three weeks or so. Supplement the information gained from sticky cards with random plant inspections. Gently blow into the flowers to detect winged adults. Look on underside of leaves for the small, less than 1/8 inch long, yellow larvae
Biology and Life Cycle: Western flower thrips develop from egg, larvae, pupae to adult. Their life cycle is dependent upon temperature, varying from 34 days at 59o F to 14 days at 86o F. Females can lay up to 300 eggs that are inserted into plant tissue.
Cultural Control: Weed control is critical because weeds harbor thrips and may be infected with tospoviruses. Inspect incoming plant material and keep isolated, if possible. Do not carry over thrips-infested stock plants or pet plants. Separate seed-grown plant material from vegetative grown material. (Tospoviruses are not seed borne). Use microscreening.
Use a fallow period, before spring production starts. Heat greenhouses until soil temperatures reach 60o F for at least 3 weeks. If greenhouses are completely weed-free, thrips will starve. Use aerosol bombs after the second week to kill any thrips emerging from the soil (pupal stage).
Biological Control: Botanigard may help to suppress thrips, especially when populations are low. Predatory mites (Neoseiulus cucumeris) are commerically available that attack young thrips larvae. Recent research at the University of Massachusetts suggests that sprinkle releases of the bulk formulation do better than sachets, especially in cropping systems with hanging baskets. Hypoaspis miles feed on thrips pupae as well as fungus gnats. Nematodes such as Steinernema feltiae may be used against thrips pupae in the soil.
Chemical Control: Rotate between classes of chemicals to delay the development of resistance. Early in the season, when populations are low, target the larvae stage with insect growth regulators such as Azatin, Ornazin, Aza-Direct, Pedestal, or Enstar.
To target the adults, thorough spray coverage with a small droplet size is needed (less than 100 microns). Time sprays to 8 a.m. or 5 p.m. when adults are most active. Two or three applications at 5- to 7-day intervals are needed to reduce populations. Marathon, and Safari may help suppress populations. Researchers have reported good control with little phytotoxicity with Conserve. Conserve tankmixed with Avid has also performed well. Mesurol, Orthene or Avid alone may also perform well for some growers.
Few new products are in development, so use effective insecticides wisely. Save Conserve to when you really need it. Rotate to a different class of insecticide after one generation (two to three weeks).
By Leanne Pundt, Extension Educator, Commercial Horticulture
Mention of particular materials is for educational purposes only and is not to be interpreted as an endorsement, nor is criticism implied of any materials not mentioned. Consult and follow registered uses listed on the label.
Casey, C. 2000. Integrated Pest Management for Bedding Plants. A Scouting and Pest Management Guide. Cornell Cooperative Extension Publication No 407. 117 pp.
Cloyd, R. 2004. Rove beetle may be an option for fungus gnat control. GMPro. Nov. 2004. 74-75.
Cloyd, R, A. and E. R. Zaborski. 2004. Fungus gnats, Bradysia spp. (Diptera: Sciaridae) and other arthropods in commercial bagged soilless growing media and rooted plant plugs. Journal of Economic Entomology. 97(2): 503-510.
Gill, S. and R. Reeser and P. Shrewsbury. 2003. Fungus Gnats and Plugs. GrowerTalks. Nov 2003. 60-70.
Gilrein, D. 2001. New Miticides for Greenhouse, Nursery and Professional Landscape Use. Plugged In. The Newsletter of the Connecticut Greenhouse Growers Association. Issue 1. pages 4-7.
Gilrien, D. 2002 What's working best? Controls for fungus gnats, thrips and mites. Society of American Florists presentation.
Lopes, P. and L. Berg Stack. 2005-2006 New England Greenhouse Floriculture Guide. A Management Guide for Insects, Diseases, Weeds and Growth Regulators. New England Floriculture, Inc.
Mahr, S., R. Cloyd, D. Mahr, and C. Sadof. 2001. Biological Control of insects and other pests of greenhouse crops. North Central Regional Publication No 581. University of Wisconsin Extension. 100 pp. http://cecommerce.uwex.edu/pdfs/NCR581.PDF
This information 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.