There are big, hairy worms and tent-like structures in my walnut tree. What are they and how do I get rid of them?
The “worms” are likely fall webworms. Fall webworms are hairy, tan to yellow caterpillars. As they feed, fall webworms construct tents or webs at the ends of branches. Tents are initially small, but the caterpillars enlarge the tents as they grow and consume the leaves within the tents. By the end of summer, tents may be 2 to 3 feet long and enclose entire ends of branches. Fall webworms feed on more than 200 species of deciduous trees. However, walnuts are their favorite host. In Iowa, the first sightings of fall webworms usually occur in early to mid-August.
Fall webworms do not cause serious damage to healthy, well-established trees. As a result, controls are not necessary. Damage to trees can be minimized by undertaking control measures as soon as the tents are discovered. Tents on branches that can be safely reached from the ground or with a ladder can be pruned out and the caterpillars destroyed. Insecticides can also be used for control, but must be applied with sufficient pressure to penetrate the tent and reach the caterpillars inside. Insecticide applications after mid-September are of no benefit and should be avoided in order to preserve predators, parasites, and other biological control organisms.