The woolly apple aphid is a tiny reddish-brown pest that invades apple trees. The "woolly" in its name is derived from a cotton-like white substance that it secretes. Woolly apple aphids can disfigure the roots, branches and bark of apple trees and can transmit disease to the fruit. You can kill woolly apple aphid colonies through natural and chemical controls.
Treat apple trees with insecticidal soap spray or diazinon-based commercial insecticides to kill off woolly apple aphids. Apply chemicals to the base of the tree in mid- to late summer when the pests have started working their way up the tree. Assess the condition after two weeks --- make a visual inspection for the aphids, their woolly cotton or their honeydew waste product on the apples and branches. Apples that have been tainted with aphids' honeydew may appear sooty or black in colour. Re-apply chemicals if evidence points to a continued infestation.
Unleash biological controls that feed on woolly apple aphids to control the problem without toxic chemicals. Parasitic wasps, lacewings and lady birds in either larval or adult states are natural enemies to woolly apple aphids. Biological controls are generally available at your local nursery. Once you release natural predators on an apple tree, the beneficial pests will spread to other affected trees naturally without human intervention.
Prune cuts in branches or bark that are infested with the pest. Branches that show galls, or swollen areas similar to knots, may indicate a woolly apple aphid problem. Large tree wounds may need to be removed to prevent the spread of the aphids instead of being repaired. Prune the affected branch above the gall or bark wound, making clean cuts to prevent further stress on the tree. Leave a collar, or small section of wood, on the branch rather than pruning the area flush to the trunk to minimise the possibility of decay.
Discourage woolly apple aphids from attacking apple trees with proper pruning. Trees with suckers, the long, thin stemlike growths that emerge from the ground near the trunk, are more likely to become overrun with these vigorous pests. Remove all suckers to help prevent an infestation.