Aphids occur on almost all types of trees and shrubs. They usually do not damage plants and are controlled by natural enemies such as lady beetles. Problems most commonly occur where aphids produce leaf curls, such as on ash, plum, honey-suckle and snowball viburnum. 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. 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. 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.