Aphids - March 8, 2006
Jeff Schalau, County Director, Associate Agent, Agriculture & Natural Resources
Arizona Cooperative Extension, Yavapai County

Right now, you may see aphids on pine and oak as well as other ornamental plants with succulent stems and leaves. Aphids have piercing-sucking mouthparts allowing them to make a good living on the flowers, leaves, stems, and sometimes roots of many host plants in our landscapes and gardens. They are soft-bodied insects that come in many shapes, sizes, and colors. The first indication of their presence may be a shiny, sticky material on the leaves. This liquid is called honeydew. Another sign is curled, stunted leaves on new growth in spring. Close inspection will usually reveal the insect itself, but donít get in a hurry to use pesticides. Aphids and the damage they cause may appear unsightly; however, they usually cause no serious, long-term harm to the plants they colonize.

Aphids can reproduce rapidly by using unique strategy. They produce young by parthenogenesis. Here female aphids lay unfertilized eggs that hatch into female young without fertilization by a male. After a few generations, they produce winged female aphids and these may fly to a different food plant. These winged females can also reproduce parthenogenetically, giving birth to winged young. Late in the season, the winged aphids return to the original food plant and some females turn into males. The males and females mate and the females lay eggs that will overwinter.

While observing, you may see ants walking among the aphids. They are probably collecting the honeydew for food. The honeydew is colorless and sticky because it contains sugars from the plant and is exuded from the anus of the aphid as waste. Some ants will protect aphids and carry them from one plant to another. In this way they cultivate honeydew. Sometimes, ants will carry the eggs to their nest for the winter and transport them to a food plant the following spring. In time, excess honeydew may build up, fungal spores in the air land on it, and sooty mold can begin growing. If left on painted surfaces, damage or discoloration can result.

Human gardeners may not appreciate the value of aphids as ants do. Even so, we should not be in a great hurry to control them with pesticides. Though Acephate and Malathion will effectively kill aphids, these insecticides will also kill beneficial predators that provide natural aphid control. Most gardeners are aware that lady beetle, antlion, and lacewing larvae are effective predators of aphids, but there are many others. Many insects including earwigs, assassin bugs, minute pirate bugs, stink bugs, soldier beetles, syrphid fly larvae, aphid flies, and parasitic wasps are natural enemies of aphids. With this assortment of "good guys," chemical control methods should only be used as a last resort to control aphids.

The simplest management tool against aphids is a good blast of water from a high pressure hose nozzle. This knocks most of them off the plant while not creating a toxic residue that would harm natural enemies. Soap sprays can also be effective at controlling aphids. To mix a soap solution, add one tablespoon of dishwashing soap or detergent to one gallon of water and apply to a small area of the plant to see if the solution will adversely affect the plant foliage. Avoid citrus scented types because they can damage the plant foliage.

Some aphids protect themselves with a waxy substance giving them a cottony white appearance. The wax protects them from the environment and predators. Other aphids cause leaves to roll and create a protective shelter for the aphids inside. These can be more difficult to control. In severe cases, pesticide application may be warranted to control these types of aphids.

If ants are tending the aphids, then it may become necessary to control the ants. Ants can be controlled by using tangle foot. If they persist, you can use baits or apply pesticides to the soil or base of plant. These strategies target the ants while limiting exposure to natural enemies. By monitoring aphid and ant populations, carefully choosing types and timing of control methods, and encouraging natural enemies, you are practicing integrated pest management (IPM).

The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at mgardener@verdeonline.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/.

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Arizona Cooperative Extension
Yavapai County
840 Rodeo Dr. #C
Prescott, AZ 86305
(928) 445-6590
Last Updated: February 28, 2006
Content Questions/Comments: jschalau@ag.arizona.edu
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