–by Dr Raymond Cloyd
The fall webworm (Hyphantria cunea) is prevalent throughout most of Kansas with webs noticeable on certain trees and shrubs. Fall webworm nests are typically quite evident, with silk webbing enclosing the ends of branches and foliage or leaves (Figures 1 and 2).
Figure 1. Fall webworm nest on birch tree (Author–Raymond Cloyd, KSU)
Figure 2. Fall webworm nest on walnut tree (Author–Raymond Cloyd, KSU)
Fall webworm larvae or caterpillars are pale-green to yellow to nearly whitish with black spots (two per each abdominal segment). Caterpillars are covered with long, white hairs (Figure 3).
Figure 3. Close-up of fall webworm larvae (Author–Raymond Cloyd, KSU)
They feed on a wide range of trees, including: birch, crabapple, maples, hickory, pecan, mulberry, and walnut. Fall webworm caterpillars, unlike eastern tent caterpillars, remain within the enclosed webbing and do not venture out to feed. Caterpillars consume leaves, resulting in naked branches with webbing attached that contains fecal deposits or ‘caterpillar poop.’
Although feeding by fall webworm caterpillars may ruin the aesthetic appeal of infested trees; the subsequent damage is usually not directly harmful to tree, especially larger trees because larger trees are primarily allocating resources for storage with less being allocated to producing new vegetative growth. However, smaller trees infested with fall webworm may look awful (Figure 4).
Figure 4. Young tree heavily-infested with fall webworm (Author–Raymond Cloyd, KSU)
The most effective means of dealing with fall webworm infestations is to simply prune-out the webs that enclose the caterpillars. Insecticide sprays may not be effective because the caterpillars remain in the webbing while feeding; thus reducing exposure to spray residues. If insecticides are used be sure to use high-volume spray applications that penetrate the protective webbing or use a rake to disrupt or open-up the webbing so that the insecticide spray contacts the caterpillars.