Alfalfa webworm (L. cereralis)
Beet webworm (Loxostege sticticalis)
Garden webworm (Achyra rantalis)
Pest description and crop damage Olive-green larvae up to 1.5 inches long, marked with black dots and both dark and light stripes down the back and along sides. If disturbed, larvae hang from leaves by silk threads.
Feeding initially appears as small transparent "windows" eaten from the undersides of leaves; later, it progresses to raggedly skeletonized and dirty, webbed leaves, especially midseason.
Scouting and thresholds No formal economic thresholds exist for webworm insecticide treatment decisions. Consider treatment if infestation levels average one to two webworm larvae on half the plants. Monitor infestations closely because webworms can defoliate plants rapidly.
Management-biological control
Several biologically based insecticides are available for webworms (Table 3).
Management-chemical control
Several post-emergence insecticides are available for webworms (Table 2).