Controlling Fall Webworms
The insect Hyphantria cunea (Drury), commonly known as the fall webworm is making its annual appearance. Look for their web-like nests at the ends of tree branches now and through late September-early October. Don't confuse the fall webworm with the eastern tent caterpillar, which rears its ugly head each spring. Where fall webworm is considered only a nuisance, the eastern caterpillar can cause serious damage to trees.
Fall webworms find homes in the branches of over 200 deciduous shade trees as well as fruit trees. In the south, the persimmon, pecan, cherry and sourwood are favorites. Webs start small, but caterpillars enlarge the tent every few days as they grow while feeding on the leaves only inside their tent. By the end of the summer, these webs can average three to four feet in size.
Webworm nests draw your attention because they are found only on the ends of tree branches. If you find multiple nest sights, don't panic. Their feeding poses no health risk to your trees because leaf loss is less important in late fall and summer. Your trees have had plenty of time to store enough food for next years leaf production.
There are two forms of fall webworms in North America; the black headed and redheaded races. The black headed caterpillars are yellow to light green and the redheaded form is tan in color. The adults are about one inch long and range from pure white to white with a few black spots.
In winter, the pupae are found in the ground, in old nest remains, under loose bark and in leaf litter. The adults emerge from late May into July. Several hundred eggs are deposited in one or two layers on the underside of leaves. The eggs hatch in about a week and the small caterpillars begin to produce a web of fine silk over single leaves. In southern states, up to four generations can occur over the summer and fall months.
Chemical controls are not recommended. These insects have over 80 natural predators and parasites that keep their numbers in check. Simply prune out the webs by hand and destroy. For taller trees, use pole pruners, a stick, or pole with a nail inserted widthwise to snag the nest.
If you are one of those people who have to spray, choose B.T. (bacillus thuringiensis variety kurstaki). This biological control is environmentally friendly and can be found in most home and garden stores under the name of BTk or Dipel. Always read and follow labeled directions carefully before using.
Complete coverage is necessary for good control. Breaking the web with a pole before spraying is necessary to increase contact of BT with the larvae. It may be necessary to use a high pressure sprayer or commercial tree service for large trees or ones that are heavily infested.
If you have webworms in your trees, devise a strategy and attack them before they get out of hand. Early recognition and proper control is necessary in order to reduce the number of insects and damage they can inflict. In late winter, we'll discuss the management of the eastern tent caterpillar.
If you have a question or need information about a plant, disease or insect found in your yard or landscape, please call the Hall County Extension Office.
Kathy Baker Seals
Horticulture Program Assistant/ Master Gardener Coordinator
Friday
May 30th, 2025
7:38PM
