By MARION BARNES
Senior County Extension Agent
You may have noticed from time to time those “oversized” spiderwebs located throughout the canopies of trees during your travels around the county. These massive webs are the nests of the fall webworm, an insect native to our state and are filled with one-inch-long caterpillars.
Fall webworms, Hyphantria cunea, are known to feed on more than 600 species of plants including row crops, herbaceous plants, shrubs, fruit and ornamental trees in orchards, nurseries and landscapes. Some common host trees include pecan, hickory, walnut, persimmon, wild cherry, river birch and sweet gum to name a few.
While these webs are unattractive in ornamental settings, they generally do not cause major damage in non-commercial settings. Healthy deciduous trees can usually tolerate late season defoliation and will resprout new foliage in the spring. However, severe infestations can cause considerable injury to smaller trees and certain situations like fruit and nut orchards. Severity of infestations vary from year to year.
The fall webworm is most active during the summer and fall months. In the spring the female moth will lay egg masses containing approximately 600 eggs on the underside of leaves. These eggs hatch in about a week and develop into red and black larva (caterpillars) covered with fine hair. Almost immediately the newly hatched caterpillars began constructing a silken web over the branch tip and begin to feed on the foliage. As the caterpillars mature, they expand the web and consume more foliage, feeding up to six weeks before pupation.
They prefer new foliage that has been exposed to sunlight. When mature, caterpillars leave the nest to pupate under bark or in the soil. The pupal stage of development can last from 12-80 days depending on environmental conditions, followed by the emergence of an adult moth. And the cycle begins again. There may be four or five generations a year in the South.
Fall webworms are susceptible to control by natural predators such as birds, spiders, parasitic wasps and small mammals. Managing fall webworms effectively includes routine inspection of trees and shrubs to detect the pest before it becomes a major problem. If control is desired and the webbing is easily accessible from the ground level, pruning and removal of the nest is one solution. Also simply breaking up the web makes the caterpillars more vulnerable to their natural enemies.
If chemical control is necessary, insecticides containing Bacillus thuringiensis (Bt) are effective when applied to small caterpillars. Control will be less successful as nest size increases. Bt insecticide products are also less toxic to many beneficial insects. Before selecting and using any pesticide always read and follow the product label and wear the recommended personal protection equipment.
For more information on the management of fall webworms check-out the Clemson Home and Garden Information Center’s Fall Webworm Management fact sheet.
Contact Marion Barnes at 843-549-2595.
