The Extension office has received numerous calls from residents concerning a strange webbing that has appeared on many trees in the area. The cause is the fall webworm, a common insect pest of trees in Gwinnett County during the early fall. The insect attacks a multitude of plants, including many fruit, nut and ornamental trees and shrubs. In some cases the webs can be so numerous they weigh down branches and cause them to break. Infestations are unsightly but rarely fatal.
Often the pest is 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.
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. 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 larvae consume leaves within the web, they expand the web to take in more and more foliage.
Checking trees that have experienced previous infestations for fall webworms 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 destroy any leaves that contain egg masses.
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 pulling the webs down. Larvae can also be knocked out of lower branches with a stick or broom, or simply pruned 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 beneficials a chance to do their job prior to spraying.
If webs are too numerous or too high in a tree to reach, sometimes insecticides, such as Sevin, 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 insectides above your head and wear all the proper protective clothing required on the chemical label. Insecticide sprays must penetrate the web deeply to be effective since the webbing is quite tough and difficult for the spray to get in. Please make sure you follow all label directions and safety precautions when applying pesticide.
But usually the insects can be controlled without insecticides. Often just ignoring them and leaving them in the trees is the best course of action since they seldom pose harm to the trees.
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.