Aphids are small (less than 1/8 of an inch long), soft-bodied, pear-shaped insects with long legs and antennae. Two of the more common species found in greenhouses include the green peach aphid (Myzus persicae) and the melon or cotton aphid (Aphis gossypii). Other species that growers may encounter include the gray cabbage aphid, the pale green foxglove aphid, and reddish-brown chrysanthemum aphid. Tulip bulb aphids can infect many different bulbs in storage.
Proper identification is important in order to choose the most effective management option. Green peach aphids (GPA) 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 with cornicles (tailpipes) at the tip of the abdomen. These cornicles are the same color as the body and only slightly darkened at the tip.
Melon or cotton aphids are generally smaller (less than 1/16 of an inch long) than green peach aphids. There is more variation in colors 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 cornicles are completely black. Growers frequently refer to melon aphids as "black aphids."
Aphids feed by inserting their stylet-like, sucking mouthparts directly into the phloem and removing plant sap. When high populations develop, plants may become stunted with curling and twisting of the young leaves. As aphids feed, a sugary plant sap, or 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. Occasionally ants may be associated with aphid-infested plants.
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.
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. In the fall, winged aphids which mate and lay eggs may appear outdoors. Aphids overwinter outdoors 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 crops are in flower. Thorough coverage by insecticides is more difficult when plants are in flower. In addition, many insecticides will cause spotting of the flowers.
Yellow sticky cards will only attract winged aphids. Place cards near the doors and vents. Focus on random plant inspections of susceptible crops and cultivars to detect the wingless 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. 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, ranunculus, salvia, snapdragon, tomato, verbena and zinnia. Some key pot plants prone to aphids include: aster, dahlia, Easter lilies, mandevilla, snapdragon and syngonium. Some key aphid-susceptible herbaceous perennials include: arabis, aubrieta, bellis, chrysanthemum, heuchera, lythrum, monarda, penstemon, phlox, salvia and viola.
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.
In the greenhouse, temperature and humidity may be manipulated in order to provide a more favorable environment for the introduction of natural enemies. Many chemical residues are harmful to natural enemies for long periods, up to several weeks or even months. Biorational materials including insecticidal soap, superior horticultural oil and neem-based materials tend to be more compatible with biological control.
Become familiar with IPM scouting techniques and have a regular monitoring program in place before attempting biological control. Become familiar with the specific environmental requirements of the natural enemy to be released. Control failures may occur if the natural enemies are released too late, at too low a rate or at a time of year when the temperature or photoperiod may adversely affect the natural enemy. Contact university specialists and commercial suppliers to gather as much up- to- date information as you can before starting a biological control program.
Natural enemies may include predators, parasitoids and pathogens. An online list of suppliers of natural enemies is available from the California Department of Environmental Protection. (See reference list for printed material).
Predators consume many prey during their lifetime. Repeated inundative releases of natural enemies are often needed in order to keep pace with the aphids' high reproductive rate in the greenhouse. A predatory midge, Aphidoletes aphidimyze, can feed on more than 60 different species of aphids. It tends to be more effective against the melon aphid than against the green peach aphid. This bright orange larva kills aphids by biting their knee joints, injecting a paralyzing toxin and then sucking out their body fluids. This midge is shipped as pupae in moist vermiculite. Adults are short-lived and tend to be active at night, so are rarely seen. 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 and will go into diapause during cool, short days. Release rates will vary with the crop grown.
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. Commercial suppliers can now supply lady beetles that are preconditioned so they are less likely to disperse after release.
The green lacewing (Chrysopa rufilabiris) adults feed on nectar and pollen. Larvae may feed on aphids, mites and whiteflies. Because larvae will feed upon each other, they must be released as far apart as possible to discourage cannibalism.
Parasitoids develop in a single host and kill the host as they grow and mature. Two species of a small, parasitic wasp, Aphidius, are commercially available. A. colemani is a parasitic wasp that attacks both green peach aphid and melon aphid. Aphidius lays its eggs in aphids and the larvae develop within the aphid. The aphid is killed as the developing larvae feed upon it. The brown, swollen exoskeleton of the aphid remains and is referred to as an aphid mummy. As the adults emerge from this mummy, one can see the small round exit hole. A related species, A. matricariae, is recommended for use against the green peach aphid.
Several types of entomopathogenic or insect-killing fungi have been developed for use against greenhouse pests. Beauvaria bassiana is a common soil borne fungus that occurs worldwide. One strain of this fungus is commercially available, Botanigard. 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. 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.
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. 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. 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.
Casey, C. Ed. 1997. Integrated Pest Management for Bedding Plants. A Scouting and Pest Management Guide. Cornell Cooperative Extension Pub. No. 407 109 pp.
Gill, S. 1995. Early detection key to aphid control. GrowerTalks. 59(2): 95.
Gilrein, D. 1995. Managing Aphids in Greenhouse Crop Production. Cornell Cooperative Extension Greenhouse IPM Update. 5(1):1-6.
Hoffman, M. and J. Sanderson. 1993. Melon Aphid. Cornell Cooperative Extension Factsheet. No. 750.50 1 pp.
Hunter, C. 1997. Supplies of Beneficial Organisms in North America. California Environmental Protection Agency, Department of Pesticide Regulation, Environmental Monitoring and Pest Management Branch. 32 pp.
Malais, M. And W.J. Ravensburg. 1992. Knowing and Recognizing: The biology of glasshouse pests and their natural enemies. Koopert Biological Systems. 109 pp.
Sanderson, J.1996. Management
of Aphids and Whiteflies. Pages 109 to 124 in Proceedings of
the 12th Conference on Insect and Disease Management in Ornamentals.
Sponsored by the Society of American Florists.
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.
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