For the past several months, trees and shrubs have endured some of the most extreme environmental conditions. A late freeze, oppressive heat and drenching rains are just a few to mention. To add insult to injury, many trees are now under attack by leaf-feeding caterpillars. Walnut caterpillars are actively stripping the leaves, leaving bare twigs and little shade behind. Here is what you need to know about how to identify and control these gregarious feeders.

As their name implies, walnut caterpillars primarily feed on black walnut, pecan and several species of hickory. However, they also are known to strip the leaves from river birch, all species of oak, willows, honeylocust and both apple and crabapple trees.

Walnut caterpillars overwinter as pupae just below the soil surface under host trees. In late spring, adult moths emerge and female moths deposit egg masses on lower leaf surfaces. There can be as many as 300 eggs per mass. By the end of June, newly emerged larvae are hungry and begin to skeletonize leaves. As they grow, the hairy brick-red colored larvae devour greater amounts of leaf tissue, leaving only the midvein. Within a month, the larvae mature and can consume entire leaves, including petioles. The mature larvae are 2 inches long and are grayish black with long grayish white hairs.

When disturbed, larvae will raise both ends of their bodies in what looks like a defensive move to ward off would-be predators. Likewise, they will crowd together in large masses on the lower part of trees and molt at the same time, leaving an ugly patch of hairy cast skins behind. Once mature, larvae drop to the ground where they enter the soil to pupate. A second generation occurs soon thereafter, giving rise to the overwintering pupae and the caterpillars we find now.

Good control begins early. When egg masses or small larvae are found, remove the leaves or twigs as a means of nonchemical control.

This may prove impractical where large trees are involved or many leaves and twigs are infested. Another nonpesticide option is to use rings of tree tanglefoot throughout the tree to trap larvae as they migrate to main branches or the tree trunk to molt. Chemical controls may provide the most practical means of control. Look for early signs of feeding on the ends of the branches. Larvae should be near by.

Readily available insecticides that do a good job are carbaryl (Sevin, Sevimol), cyfluthrin (Decathlon, Tempo) and azadirachtin (BioNeem, Margosan-O). As always, read and follow all label directions.

If all else fails, do nothing. Because they are only leaf-feeding insects, they will strip the leaves and stop there. This late in the season, no damage is done to the tree, and it means less leaves to rake this fall.