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Aphids |
By Judy Sedbrook, master gardener, Colorado State University Cooperative Extension, Denver County
Aphids are very common. Sometimes called plant lice, they are small, soft-bodied, pear-shaped insects, generally less than 1/8" long. Most are green or black but they can also be found in a variety of other colors as well. A characteristic common to all aphids is the presence of cornicles, or tubes, on the back ends of their bodies, sort of like "tailpipes". These cornicles secrete substances that help protect the aphids from predators. Over winter, aphids exist as eggs on perennial plants and hatch in the spring.
Aphid larva
The insects cause injury to plants by sucking the sap and juices from the soft, new growth.This damages the host plant's ability to properly process food and causes the plant to lose vigor, wilt, distort or show spots. Aphids also can infect healthy plants with viral diseases they have picked up from unhealthy plants.
They often live in large clusters or colonies and are found together with ants. The ants feed on the honeydew produced by the aphids and protect the aphids in return, often keeping their eggs through the winter in their nests. In the spring, the ants transport the aphids to host plants and then protect them from enemies.
Aphid colony on rose
The honeydew is a sticky, sweet substance that is produced by the aphids when they can't use all of the sugar taken from plants. It can drip from infested trees or shrubs onto cars, sidewalks, and porches creating quite a mess. You may see a black, sooty mold growing on it.
Aphids are most likely to be a serious problem in situations where they are protected from their natural enemies: either in an enclosed area like a greenhouse, or when their natural enemies have been destroyed by insecticides.
Natural enemies play an important part in controlling aphids. Lady beetles, lacewings, damsel bugs, flower fly maggots, certain parasitic wasps, birds, and fungal diseases all attack aphids.
CONTROLS:
Biological Control:
- Ladybugs prey on aphids, control small infestations and can be added to your garden. You can avoid the use of chemical sprays if predators are abundant.
- Control ant populations by setting traps or destroying colonies.
- Fungi that attack aphids are also becoming commercially available. The control achieved with these insect pathogens may be dependent on environmental conditions (humidity or moisture and temperature).
Cultural Control:
- Hose aphids off of infested plants with a heavy spray of water. Take care not to use so much pressure that it will injure delicate plant parts.
- Prune off and destroy heavily infested plant parts.
- Most aphids can be controlled with the use of insecticidal soaps. Insecticidal soaps are non-toxic and safe to use in backyards.
Chemical Control:
- Many aphids are resistant to chemical insecticides and using insecticides may cause aphid outbreaks.
- Some species can be controlled with neem (azadirachtin) and some with malathion. Whenever using pesticides, be sure to read and follow the directions and heed the cautions found on the label.
Prevention:
- Spray fruit trees in the spring with dormant oil.
- Aphids are attracted to yellow. Try placing a sticky yellow-color trap nearby to lure the aphids away from plants.
- Avoid the use of high-nitrogen fertilizers. Aphids thrive when the nitrogen in the plant sap is high.
For more information on Aphids, see CSU Fact Sheet 5.511.
Photographs courtesy of Judy Sedbrook.
