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Aphids

Are you finding ants on your aspen or cottonwood trees?  Is there a sticky “sap-like” substance on your walkway, car or patio furniture? If these problems sound familiar, your trees are likely infested with aphids.

 

The following information is based on the Colorado State University Service in Action Sheet by Whittany Crenshaw, an Entimologist at Colorado State University.

 

Quick Facts...

• Aphids occur on almost all types of trees and shrubs. They usually do not damage plants but the aphid honey dew can be an inconvenience when the sticky aphid excretion lands on cars and outdoor furniture. 

 

• Problems most commonly occur in Summit and Eagle Counties when aphids produce leaf curls, on trees such as cottonwoods and aspen trees.
• Check for natural enemies before treating with insecticides.
• Systemic insecticides are particularly effective when aphids have curled the leaves.
• Contact insecticides and soaps are useful when aphids are exposed on leaves.

 

Description

Aphids are small insects, typically less than 1/8 inch, although some may be almost 1/4 inch long. Colors range from bright orange or red to dull gray. One common group, woolly aphids, produces an abundance of flossy, waxy threads that cover their bodies. Winged and wingless forms can be produced by all Colorado aphid species (Figure 1).

Aphids feed on plants by sucking plant sap from the leaves, twigs or stems. When abundant, aphids remove large quantities of sap, reducing plant growth and vigor. Aphids feeding on developing leaves also can produce leaf curl injuries.

Most aphids excrete large quantities of a sweet, sticky substance called honeydew. At times, excessive honeydew dropping from trees can be an extreme nuisance. Also, sooty mold fungus may grow on the honeydew, producing a gray, unattractive covering of the leaves. Sooty mold is not damaging to the trees except when it covers leaves and temporarily reduces photosynthesis.

Ants often are attracted to honeydew and feed on it. Ants may even tend aphids and other honeydew-producing insects (certain scales, leafhoppers, treehoppers), protecting them from natural enemies such as lady beetles and lacewings. Often the presence of ants crawling up trees or on foliage indicates that large numbers of aphids or other honeydew producers also are on the plants.

                                 

Birch Aphid                                                                        Giant Conifer Aphid   

Typical Aphid Life History

Most species of Colorado aphids over winter as eggs on specific types of woody plants. Eggs hatch in the spring. The following spring and summer, forms of the aphid sometimes move from overwintering plants to other plant species. Summer aphids consist entirely of females that give birth to live young at a rate of one to 20 per day.

The newly hatched aphids can complete their development within one to two weeks, after which they begin to produce more aphids. Consequently, aphid populations may increase rapidly, with several generations occurring during the growing season. At the end of the summer, both male and female aphids are produced. They mate on the overwintering host plant, and females lay eggs.

Control

Many kinds of insects naturally prey upon aphids. Most common are various species of lady beetles (ladybugs), green lacewings, syrphid flies and small parasitic wasps. Under many conditions, these beneficial insects provide effective control of aphids. Before applying any insecticide, check the plants to make sure these natural controls are not already reducing aphid numbers. Sometimes ants interfere with these natural controls. Excluding ants with sprays, sticky bands, etc., can allow biological controls to be effective.

 

When natural enemies are not abundant enough to provide aphid control, insecticides sometimes are needed to prevent plant injury. For most aphid problems, particularly those associated with leaf curls, insecticides that move systemically within the leaf or plant provide the best control. The most common systemic insecticide available to homeowners is Orthene (acephate). Cygon (dimethoate) also may be available as a spray for use on evergreens.

 

DiSyston is a systemic insecticide sold in granular form, or as a plant food mixture that can be mixed with soil and picked up by plant roots.

Most systemic insecticides are quite toxic to people; use with extra caution. Some plants may be injured by certain systemic insecticides. Carefully read and follow all label directions. None of the systemic insecticides available to homeowners can be legally used on food crops.

Contact insecticides that do not move systemically in plants are useful for aphid control where the insects are exposed on the plants. Contact insecticides for aphid control include Malathion, Diazinon and Dursban. Plant coverage must be thorough when using contact insecticides. Diazinon is extremely hazardous to birds, so use with extra caution on plants frequented by birds for nesting or feeding. Sevin (carbaryl) is effective against most woolly aphids found on evergreens, but has limited effect on most other aphid species.

On tolerant plants, insecticidal soaps can provide aphid control. Soaps typically have a low residual and require several applications during a season. Always test soap or detergent on a small area of the plant because these products may injure plants.

Aphid problems originating from eggs that overwinter on the plant also can be controlled with dormant oils.

Where high water pressure is available, infested plants may be hosed with water to reduce aphid numbers. This also removes recently deposited honeydew.

A Cut Above Forestry does have pesticides available for owner application at our Breckenridge Office.  Should you prefer not to apply the chemicals yourself, we can recommend a competent, licensed applicator