Jim Downs (Forestry Field Specialist, OSU Extension) is reporting a localized Fall Webworm (Hyphantria cunea, family Erebidae) outbreak in Logan County, OH. The heavy infestation was first observed and reported to Jim by Jacob King (ANR Extension Educator/LCSWD Educator, OSU Extension, Logan County).
Jake estimated that at least 200 acres of woodlands are being impacted. Jim noted that black walnut (Juglans nigra) is the most heavily affected, followed by American elm (Ulmus americana), American plum (Prunus americana), Amur honeysuckle (Lonicera maackii), bitternut hickory (Carya cordiformis), black cherry (Prunus serotina), and white mulberry (Morus alba).
The population explosion appears to consist largely, or entirely, of the red-headed fall webworm biotype. The fall webworm life cycle, feeding behavior, and differences between the black-head and red-headed biotypes are described in a BYGL Alert titled, “Fall Webworm Nests Return,” posted on August 7 and available by clicking this link:
https://bygl.osu.edu/node/2539
The photos Jim took while visiting the site illustrate the magnitude of the outbreak. Numerous large nests are appearing in tree canopies with some trees encased in heavy webbing.
The red-head fall webworm biotype has a history of producing localized outbreaks in Ohio. In 2021, Yellow Springs suffered a dramatic outbreak of red-headed fall webworms that affected almost every black walnut in and around the village in Greene County, OH.
Trees were sheathed in silk and defoliated. The webworms demonstrated an unusual feeding behavior by leaving their nests and feeding in the open after exhausting their silk-encased food supply. Here is the BYGL Alert posted in 2021 documenting the Yellow Springs outbreak:
https://bygl.osu.edu/node/1848
A Message from Management
Our native fall webworm must survive a gauntlet of natural enemies consisting of predators, parasitoids, and pathogens (3-Ps) to produce outbreaks. Consequently, these dramatic population explosions are usually rare and highly localized.
Equally important, outbreaks usually “crash” after one season owing to the collective impacts of the 3-Ps. Indeed, fall webworms did not make an encore appearance in Yellow Springs in 2022. There was only a spattering of nests outside of the village. Also, the growth rates of the walnut trees appeared unaffected by the outbreak.
Fall webworms normally have a minimal impact on overall tree health, making late-season efforts to control the outbreaks unwarranted. Although fall webworms produce two generations per season in Ohio, the accumulated tree defoliation does not become dramatic until after trees have had enough time to produce and store enough carbohydrate to support new growth next season.
