The fall webworm, Hyphantria cunea, is a common pest of trees in Henderson County. The caterpillar attacks more than 88 different kinds of plants, including many fruit, nut, and ornamental trees and shrubs. They especially like sourwoods. The webs can be so numerous they weigh down branches and cause them to break.
Fall webworms are notorious for the large conspicuous webs they produce. Heavy infestations are unsightly but rarely fatal. If the caterpillars attack the same tree repeatedly over several years, they can stress the plant make it more susceptible to drought, disease or other insect pests.
The fall webworm is a caterpillar; the larval stage of a small white moth. Full-grown caterpillars are approximately 1-inch long, pale green or yellow, and covered with tufts of long, white and black hairs.
Fall webworms often cover entire branches with their webs. In extreme infestations whole trees may be covered. Larvae feed within the web, eating leaf tissue between the leaf veins. When cooler temperatures herald the coming of fall, the larvae begin to enclose themselves in cocoons. They spend the winter as pupae in these silken cocoons on the ground or on tree bark. In the spring, the moths emerge from their cocoons, disperse and mate. Female moths deposit their eggs on the undersides of the leaves of plants they like to eat.
Soon after webworm eggs hatch the larvae begin to build a web. As larvae consume leaves within the web, they expand the web to take in more and more foliage. The nest grows as acquire more leaves.
Scouting for Fall webworms on trees that have experienced previous infestations is recommended. Remove any old nests and leaves from under the tree to reduce the amount of pupae that will emerge in the spring. Locate, remove and destroying any leaves that contain egg masses.
The caterpillars can be controlled without insecticides. Larvae may be knocked out of lower branches with a stick or broom. Many birds and beneficial insects attack the egg and larval stages of fall webworm. You can help these predators and parasites get to their fall webworm prey by tearing open the webs. Webs can also be pruned from smaller branches; dispose of nests in the trash.
Fall webworms do not kill trees. Remember that insecticides usually kill all insects. So give the beneficial insects and birds a chance to do their job and avoid applying chemicals.