Throughout our area, mysterious webs have begun to appear in the outer branches of many trees. The cause is the fall webworm, an insect pest of trees during the early fall. The insect attacks a multitude of plants, including many fruit, nut, and ornamental trees and shrubs. Pecan trees are one of their favorites. In some cases, the webs can be so numerous they weigh down branches and cause them to break. Though unsightly, the infestations are rarely fatal.
Often these insects are confused with the Eastern tent caterpillar, which makes webs early in the year in the crotches of the trees. Fall webworms make their webs in the outer limbs of the trees in the late summer and early fall.
The fall webworm is a caterpillar. Full-grown caterpillars are approximately 1-inch long with a pale green or yellow color, and they are covered with tufts of long, white and black hairs. Fall webworms often cover entire branches with their webs. Larvae feed within the web, eating leaf tissue between the leaf veins. As the weather becomes colder, the larvae begin to enclose themselves in cocoons, and they spend the winter as pupae in 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. The webworm eggs hatch later in the season and the larvae begin to build a web. As the larvae consume leaves within the web, they expand the web to take in more and more foliage.
The caterpillars can often be controlled without insecticides. You can destroy the webs by using a long pole with a hook on the end and pull the webs down. Larvae can also be knocked out of lower branches with a stick or broom, or simply cut out. Many 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. Remember, insecticides usually kill all insects, so give the beneficial ones a chance to do their job instead of spraying. Often just ignoring fall webworms and leaving them in the trees is the best decision because they seldom pose harm to the trees.
If webs are too numerous or too high in a tree to reach, sometimes insecticides can be used to kill the insects. Hose-end sprayers or commercial high-pressure sprayers are best for reaching upper portions of tall trees. Use caution when applying insecticides above your head. Make sure you wear all of the proper protective clothing required on the chemical label. To be effective, the spray needs to penetrate deeply into the webbing. Please make sure you follow all label directions and safety precautions when applying pesticide.
Fall webworms may not be attractive, but they do not harm the trees they infest. Usually the best course of action is to leave the insects alone, and they will eventually go away.
Timothy Daly, is an Agricultural and Natural Resource Agent with Gwinnett County Extension. He can be contacted at 678-377-4010 or firstname.lastname@example.org.