Fall Webworm – Generation II

The second generation of fall webworm is underway and their distinctive silk nests should be abundant in many areas through August. These fuzzy caterpillars have pale green or yellow hairs over their bodies with rows of black spots along their backs. They cooperatively build light gray tents (Figure 1) that enclose the ends of branches of over 100 species of forest trees. shade trees, and shrubs. Sourwood, pecan, and persimmon are favorite hosts. Fall webworms feed on leaves inside the webbing and expand the “tent” as they require more food during their 4 to 5 week developmental period.

Figure 1. Fall webworm tents were particularly abundant on sourwood trees in Powell County on July 16 this year. Leaves can appear “scorched” from surface feeding of small caterpillars (Photo: Lee Townsend,UK)

Figure 1. Fall webworm tents were particularly abundant on sourwood trees in Powell County on July 16 this year. Leaves can appear “scorched” from surface feeding of small caterpillars (Photo: Lee Townsend,UK)

Figure 2. Larger fall webworm caterpillars cause more extensive defoliation (Photo: Lee Townsend, UK)

Figure 2. Larger fall webworm caterpillars cause more extensive defoliation (Photo: Lee Townsend, UK)

Management

The presence of fall webworms is primarily an aesthetic issue on a healthy, established landscape tree.   However, significant infestations on stressed or new transplants can be serious.

  • When practical, remove and destroy unsightly webs and the resident caterpillars.
  • A Bt-spray can be effective against small caterpillars (1/2-inch long or less). This insecticide is a stomach poison webworms, so it must be applied to foliage on which they are feeding. Products containing spinosad or pyrethroids can work as contact or stomach poisons. Treatments can be focused on the foliage in and around the tent. Usually, there is no need to spray entire trees.
  • Fall webworm has significant natural enemies. Several spider species feed on the caterpillars and some beneficial wasps use them as hosts.

 

By Lee Townsend, Extension Entomologist

 

Posted in Forest Trees, Landscape Trees & Shrubs