–by Dr. Raymond Cloyd
The first generation of fall webworm (Hyphantria cunea) is now prevalent in most of Kansas with webs present on certain trees. Fall webworm nests are very noticeable, with silk webbing enclosing the ends of branches and foliage or leaves (Figures 1 and 2).
Fig 1. Fall webworm nest on walnut tree (Auth–Raymond Cloyd, KSU
Fig 2. Fall webworm nest on birch tree (Auth–Raymond Cloyd, KSU
Fall webworm larvae or caterpillars are pale-green, yellow to nearly white, with two black spots on each abdominal segment. Caterpillars are covered with long, white hairs (Figure 3).
Fig 3. Close-up of fall webworm larvae (Auth–Raymond Cloyd, KSU)
Fall webworm caterpillars 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.’ These nests will eventually dry-up as the caterpillars pupate, with adults’ eclosing (emerging) from pupae later on.
Feeding by fall webworm caterpillars may ruin the aesthetic appeal of infested trees; however, the damage is typically not directly harmful to trees—especially larger trees. The most effective method of dealing with fall webworm infestations is to simply prune-out the webs that enclose the caterpillars, place into a plastic bag, and dispose of immediately. 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.