By Eddie Ayers, County Extension Agent
I know it’s hard to believe but yes, the days are actually getting shorter and shorter and thus I’m already getting a lot of calls about the appearance of webbing in trees around the county. This webbing is home to a caterpillar called the fall webworm. They use the silk webbing to form protection from predators as it feeds on leaves of over 100 different types of trees. Some of the most common trees we see them infest are cherry, black walnut, mulberry, elm, sweet gum, willow, apple, ash, and oak. It is a native insect that ranges from Canada to Mexico. The signs of fall webworms in a tree are relatively easy to spot. They will create a nest at the end of branches and as they need more leaves, they expand the size of the nest to meet their needs.
In general fall webworms are nothing to be too concerned about. If a tree is healthy, it will be able to withstand an infestation. Most deciduous trees can tolerate losing most of its leaves, especially during this time of year when fall leaf drop is really just around the corner. The time to be concerned with fall webworms is when small trees are trying to become established or when trees are sick or stressed. The extra stress of losing too many leaves can really affect those trees but in general, the damage they cause in hardwoods is mostly cosmetic and does not cause long term damage to the health of the tree, except in the stressed trees mentioned above.
With that in mind, chemical control is generally not required but if you feel the need to treat an infestation, start with insecticidal soaps, horticultural oils or bacillus thuringiensis. These products will provide control of the caterpillar when it is small and won’t harm other insects or predators who feed on them. However, if you have large caterpillars on a tree, you need to consider using an insecticide such as carbaryl (Sevin), bifenthrin, pyrethroids, or cyfluthrin. When using any of these products, remember to always read and follow the labeled directions, and do not spray when there is bee activity in the area.
In order for the insecticide treatment to be effective, you must make contact with the fall webworms inside the webbing or on leaves next to the webbing that will serve as the next meal for the caterpillars. Be prepared to break into the web nest to expose the mass of caterpillars inside. This can be done with a stick if you can reach it, or by throwing something like a ball through it, or if local laws allow it, shooting it with a shotgun. Spraying the outside of the webbing will not provide acceptable control.
Another method of control is to break open the web and pull the whole thing completely out of the tree, letting it fall to the ground. This exposure will allow predators to feed on the exposed caterpillars. And I have heard of people burning the web home, but that can be a dangerous activity for you and the tree.
I have also had a couple of people say that the name fall webworm is misleading since we have been seeing them in late July and early August this year and it’s not “technically” fall yet but the reason their timing this year is a little early is because of the heat we’ve experienced this summer. With warm temperatures, they’ve completed their life cycle earlier. However, having them appear in July and August also means they will soon be gone from our trees and we can look forward to some brilliant colors when it really is fall.
For more information, contact me at the Gilmer UGA Extension office.