Managing Aphids in the Greenhouse
Aphids can be serious and persistent pests in the greenhouse. They are difficult to control due to their high reproductive capability and resistance to many different insecticides. Aphids are sucking insects that can cause curling and distortion of tender young growth. The presence of aphids, their white shed skins and honeydew can reduce the aesthetic quality of a wide range of greenhouse crops.
Aphids are small (less than 1/8 of an inch long), soft-bodied, pear-shaped insects with long legs and antennae. Cornicles, “tail pipe like” protrusions, can be seen at the rear of their abdomen. Some of the most common species found in greenhouses include the green peach aphid (Myzus persicae), the melon or cotton aphid (Aphis gossypii) and the foxglove aphid (Aulacorthum solani). Potato aphids (Macrosiphum euphorbiae) may occasionally occur. Other species that growers may encounter include the gray cabbage aphid, the bright yellow-orange oleander aphid, and the reddish-brown chrysanthemum aphid. Tulip bulb aphids can infect many different bulbs in storage. Some aphids may even be found on plant roots (Pemphigus species).
Proper identification is important in order to choose the most effective management option. Aphids vary in color depending upon the plants they are feeding on, so should not be relied upon to identify species.
Green peach aphids have red eyes and may vary in color from pale yellow to green to pinkish-red. The pear-shaped adults are approximately 1/14 of an inch long. They have long cornicles that are approximately the length of their body and only slightly darkened at their tip. Green peach aphids also have a pronounced indentation between the base of their antennae.
Melon or cotton aphids are generally smaller (less than 1/16 of an inch long) than green peach aphids. There is more variation in color within the same aphid colony. Melon aphids may be yellow to green to purplish-gray to black with distinctive white patches on the abdomen. Their short (approximately 1/3 of an inch long) cornicles are completely black. Melon aphids have antennae that are shorter than their body. Melon aphids do not have a distinct indentation are the base of their antennae like the green peach aphid. Growers frequently refer to melon aphids as "black aphids."
Foxglove aphids are also known as the glasshouse potato aphid. The pale green, shiny foxglove aphids have large dark green spots at the base of their cornicles. They also have black markings on their leg joints and antennae. Foxglove aphids also have an indentation between their antennae. They are larger in size than the green peach aphids, (.11 of an inch) long. (Photo credit, Dan Gilrein, Cornell)
Potato Aphids are long slender aphids with antennae longer than their body. They are usually green but may be pink or red with a dark longitudinal stripe. Potato aphid’s long cornicles are light brown in color with a dark tip and are also curved outward. Potato aphids also have an indention between the base of their antennae.
Root aphids resemble root mealybugs because they are covered with white wax. However, they are smaller than root mealybugs and have reduced ring like cornicles which are located on the end of their abdomen.
Aphids feed by inserting their stylet-like, sucking mouthparts directly into the phloem and removing plant sap. When high aphid populations develop, plants may become stunted with curling and twisting of the young leaves. As aphids feed, a sugary plant sap, known as “honeydew”, is excreted. Honeydew promotes the growth of black sooty mold fungi which can then reduce photosynthesis. As aphids molt, their whitish cast skins may also detract from the aesthetic quality of many crops. Growers may mistake these shed skins with whiteflies. Occasionally ants may be associated with aphid-infested plants.
Transmission of Viruses
In agricultural production, aphids are responsible for the transmission of a number of plant-infecting viruses. In the greenhouse, direct feeding damage is generally of more concern than virus transmission. However, aphids have been reported to transmit cucumber mosaic virus which can cause flower break and distortion on cyclamen, lisanthus and vinca.
Life Cycle of Aphids
Most types of aphids found in greenhouses do not mate. All of the aphids present are females which can give birth to live nymphs. There is no egg stage. An adult female may live for up to one month. During this time, she may give birth to 60 to 100 live nymphs. Migratory winged aphids may appear when the colony becomes overcrowded or when the food supply is depleted so they can find a new food source. Outdoors, aphids overwinter in the egg stage.
Inspect incoming plant material and cuttings for signs of aphids. Many aphid outbreaks occur when herbaceous perennials are introduced into the greenhouse from the overwintering cold frames. Aphids may also be carried inside on clothing or blown into the greenhouse through doors or vents.
Aphid-infested weeds under the benches are frequently a source of recurring aphid problems. Inspect and remove weeds promptly. Use a weed mat barrier to prevent weed growth under the benches. The use of excessive nitrogen promotes lush growth that is favorable to aphid development.
A regular, weekly scouting program is needed to detect aphids early before populations explode.
Focus on random plant inspections of susceptible crops and cultivars to detect the wingless aphid nymphs. Look for whitish-cast skins and honeydew. Green peach aphids tend to be spread more evenly throughout the crop whereas melon aphids tend to be found in isolated hot spots. Melon aphids are also less likely to form winged adults. They usually stay on the lower leaves and along the plant stem. Foxglove aphids inject toxic saliva as they feed leading to curled and distorted leaves, and early leaf drop. Foxglove aphids also tend to drop off of the leaves so may be hard to find. Because foxglove aphids reproduce faster at 50˚ to 60˚ F than at 77˚ F they are more of a problem when crops are grown cool or in the spring.
Look on the leaf undersides and buds of aphid-susceptible crops. Some key bedding plants prone to aphids include: ageratum, alyssum, celosia, chrysanthemum, dahlia, gerbera daisy, herbs (many types), fuchsia, hydrangea, impatiens, pansy, pepper, portulaca, primula, salvia, snapdragon, tomato, verbena and zinnia. Some key pot plants prone to aphids include: aster, dahlia, Easter lilies, mandevilla, snapdragon and poinsettia. Some key aphid-susceptible herbaceous perennials include: arabis, aubrieta, bellis, chrysanthemum, heuchera, monarda, penstemon, phlox, salvia and viola.
Yellow sticky cards will only attract winged aphids that have entered the greenhouse from outdoors, especially during the spring and early summer. Or they may indicate an aphid infestation within the greenhouse that resulted in winged aphids. However, they are not a reliable indicator of population levels in the greenhouse.
In outdoor production, natural enemies, including ladybird beetles, lacewings, syrphid flies, small parasitic wasps and fungal diseases, may provide a degree of control. Outdoor environmental conditions, such as wind, rain and freezing temperatures, can also reduce aphid populations.
Commercially available natural enemies may include predators, parasitoids and pathogens. In general, with the exception of the aphid predatory midge, most predators are not as effective as parasitoids in maintaining aphid populations at acceptably low levels.
Repeated inundative releases of natural enemies are often needed in order to keep pace with the aphids' high reproductive rate in the greenhouse. The goal of these repeated releases is an immediate suppression of the pest as compared to the establishment of a self reproducing population (inoculative releases). Aphids reproduce rapidly so hot spots of aphid activity may occur and need to be treated with an alternative pesticide that is compatible with the particular natural enemies released. Consult with your supplier or check the side effects databases online.
Predators consume much prey during their lifetime. A predatory midge, Aphidoletes aphidimyze, can feed on more than 60 different species of aphids. This bright orange larva kills aphids by biting their knee joints, injecting a paralyzing toxin and then sucking out their body fluids. Aphidoletes is shipped as pupae in moist vermiculite; adults will emerge in 7 days at 72 ˚F. Adults are short-lived and tend to be active at night, so are rarely seen. After mating, a female predatory midge can lay up to 250 eggs over a 10 day period. Eggs are laid among the aphids, and hatch into larvae after 2 to 3 days. Larvae feed for 3 to 5 days. Larvae drop to the ground to pupate, so sawdust, peat or holes in the weed mat barrier on the ground are needed to provide pupation sites.
This midge is most effective in the summer. It will go into diapause (a resting period of inactivity) during cool, short days (less than 8 hours of daylight). This can be prevented by the use of low intensity lights during the short days. Greenhouse temperatures should be between 60 and 80˚ F and 50 to 85% relative humidity. Release rates will vary with the crop grown but should be made at the first sign of aphid damage and repeated weekly until predators establish. Apply Aphidoletes in the early morning or evening near aphid colonies. Aphidoletes aphidimyza may be used preventively in combination with aphid parasitoids. Because you rarely see the adults, look for fed upon aphids (shriveled brown or black) as evidence of their activity.
The green lacewing (Chrysopa rufilabiris) adults feed on nectar, pollen and honeydew. They are usually active at night. Larvae (also known as “aphid lions”) feed on aphids, thrips, spider mites and whiteflies, mealybugs and other soft bodied insects. They are commercially available as eggs or larvae. The adult can lay up to 600 eggs. Larvae will emerge from eggs in 3 to 4 days at 75 to 80˚ F and pupate about 14 days later. Adults emerge in 5 days. Eggs are laid individually at the end of hair like filaments on plant foliage. Larvae are quicker acting than eggs and aphid populations may be reduced in about two weeks.
Ideal temperature is between 75-79˚ F with the minimum in temperature for activity of 60˚ F. Repeat applications are often needed. The larvae tend to hide in the plant canopy during the day, but you can easily see their eggs on the foliage.
A lady beetle (Hippodamia convergens) feeds on many different types of aphids and other soft bodied insects. Eggs are laid near prey and the larvae may consume from 500 to 1000 aphids. Lady bird beetles are difficult to establish in the greenhouse. Although they are inexpensive and can be easily stored in the refrigerator, they are additional concerns with their use. Hippodamia convergens are collected from the wild, so you are depleting lady bird beetles from their natural habitat. Some lady bird beetles may have been parasitized by a small wasp (Perilitus coccinellae) that as they leave the greenhouses, could potentially infect native ladybird beetles.
Parasitoids develop in a single host and kill the host as they grow and mature. Different Aphidiusspeciesarecommercially available. Aphidius lays its eggs in aphids and the larvae develop within the aphid. The aphid is then killed as the developing larvae feed upon it. The swollen exoskeleton of the aphid remains, which is referred to as an “aphid mummy.” As the adults emerge from this mummy, you can see the small round exit hole. A. colemani is a parasitic wasp that attacks both green peach aphid and melon aphid. A related species, A. matricariae, attacks the green peach aphid. A. ervi, is used against larger species, such as the foxglove and potato aphids. Aphelinus abdominalis is a parasitic wasp that is used to control larger species of aphids such as the potato aphid. Suppliers also offer a mix of different species if you have a number of different aphid species present or are unsure of their identity.
Aphid Banker Plant Systems
Aphid Banker plant systems are a mini rearing system supplying a non pest species of aphid (a cereal aphid known as the bird cherry oat aphid (Rhopalosiphum padi) grown on grain plants (barley, wheat or oats) for the Aphidius colemani populations to build up and disperse thru the greenhouse.
For more specific directions and information, see Aphid Banker Plant System for Greenhouse IPM, Sept by Step.
Many growers have been using screened cages for their aphid banker plants. Some have been experimenting with using hair nets placed directly over the containers of banker plants. But, some growers have mentioned that the holes in hair nets are too large, allowing the parasitic wasps (Aphidius colemani) to contaminate the aphid population too soon, before the cereal aphid populations have build up. To solve this problem, Lloyd Traven from Peace Tree Farms, says he uses “Keystone Adjustable caps” which have a tighter weave and he doubles the net. He says they cost about .30 per banker plant. A. colemani will cluster on areas where banker plants are grown trying to get to the aphids so he uses compressed air blasts to remove them for a while to get in to work with plants.
Several types of entomopathogenic or insect-killing fungi have been developed for use against greenhouse pests. Two commercially available types are Beauveria and Paecilomyces.
Beauvaria bassiana is a common soil borne fungus that occurs worldwide. Fungal spores (conidia) infect the insect through the insect's cuticle. The fungus secretes enzymes which dissolve the insect's cuticle. After it enters the insect's body, the fungus produces a toxin that weakens the insect's immune system. This fungus requires high relative humidity and moderate temperatures (65-75˚ F) for 8 to 10 hours in order to be effective. Beauveria may not be compatible with the convergent ladybird beetle (Hippodamia convergens) depending upon the concentration of spores applied.
Thorough spray coverage is needed so that the fungal spores contact the targeted insect pest and begin the infection process. Repeated applications (three to five) may be needed for effective control.
Paecilomyces fumosoroseus is a naturally occurring fungus found in infected and dead insects and some soils. The fungus infects the insect by penetrating the outer layer (cuticle) of the insect. It works best at temperatures between 72 and 86˚F and high humidity.
Aphids are difficult to control with insecticides for a number of reasons. Control failures may be due to poor spray techniques, inadequate coverage or high pH in the spray tank. If aphids are present on flowers, systemic insecticides won’t be able to move into the flowers. Aphids may be difficult to reach if they are on the underside of the lowest leaves (common with foxglove aphids). Among green peach aphid populations, resistance to organophosphates, carbamates and pyrethroid insecticides has been reported. Winged forms of the melon aphid are more resistant to organophosphate pesticides than wingless forms. Different strains of aphids may be resistant to different materials. Use pest-infested plants as indicators to monitor the effectiveness of treatments in your individual situation. Systemic materials may be more effective because aphids tend to ingest large quantities of plant sap, especially if applied before plants are in flower. Thorough coverage of the underside of leaves is needed for contact materials. Two applications of contact sprays may be more effective than one treatment. Consult the most recent edition of the New England Floricultural Crop Pest Management and Growth Regulations Guide: A Management Guide for Insects, Diseases, Weeds and Growth Regulators for more specific guidelines. Available from Northeast Greenhouse Conference and Expo and the UConn CANR Communications Resource Center.
Casey, C. Ed. 1997. Integrated Pest Management for Bedding Plants. A Scouting and Pest Management Guide. Cornell Cooperative Extension Pub. No. 407 109 pp.
Gilrein, D. 1995. Managing Aphids in Greenhouse Crop Production. Cornell Cooperative Extension Greenhouse IPM Update. 5(1):1-6.
Gilrein, D. G, 2008. Choose the most effective aphid controls. GMPRO. May 2008 51-55.
Hoffman, M. and J. Sanderson. 1993. Melon Aphid. Cornell Cooperative Extension Factsheet. No. 750.50 1 pp.
Hunter, C. 1997. Suppliers of Beneficial Organisms in North America. California Environmental Protection Agency, Department of Pesticide Regulation, Environmental Monitoring and Pest Management Branch. 32 pp.
Jandricic, S. and J. Sanderson, 2011. Early Season Pest Threat. Greenhouse Canada, 12-14.
Malais, M. And W.J. Ravensburg. 2003. Knowing and Recognizing: The biology of glasshouse pests and their natural enemies. Koppert Biological Systems. 288 pp.
Sanderson, J. Greenhouse Aphid Management.
Skinner, M, C. Frank and R. Valentine. 2011. Aphid Banker Plant System for Greenhouse IPM, Sept by Step.
Thomas, C. Greenhouse IPM with an Emphasis on Biocontrols.
This information was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate.
By: Leanne Pundt, Extension Educator, University of Connecticut, Revised 2011
The information in this document is for educational purposes only. The recommendations contained are based on the best available knowledge at the time of publication. 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. The University of Connecticut, Cooperative Extension System, College of Agriculture and Natural Resources is an equal opportunity program provider and employer.