Overview:Also known as subterranean sod webworm, these lawn moths are now reaching peak flight in most lawns along the Wasatch Front. Light tan during short, low flights, they practically disappear after landing. Sneak up on one to see a surprisingly showy ½”-long insect. During the 6 to 8 weeks between mid-June and mid-July, SSW’s presence is obvious as you walk across your lawn. Adult moths flush from their grass blade perches, fluttering only a short distance to land again. Adult moths cause no damage, they simply fly, mate, and lay eggs. As with many moth-type insects, control is targeted on the immature insects. Larvae (caterpillars) hatch from eggs through July and chew on grass crowns from July through September. As temperatures drop in October, each larva spins a silken case in the turf. Through winter, larvae rest in a suspended state. As temperatures rise in late spring, they pupate. Adult moths emerge in May or early June. There is only one generation of these insects per year. “I would say billbugs and white grubs seem more problematic”, notes Dr. Diane Alston, USU Extension entomology specialist. “But the subterranean sod webworm seems to be becoming a bigger issue.” Alston recently heard feedback from a group of about 150 landscape professionals, many of whom had questions about controlling this pest. Subterranean sod webworm is controlled effectively by Bacillus thuriengiensis (B.t.), an organic pesticide available by various trade names at most garden centers. For best results, Alston recommends “Don’t scrimp on the B.t. Apply it at the full rate recommended on the label. The larvae must eat it to be killed.” Application by hose-end sprayer may work best, since the volume of water will help carry the pesticide down into the grass crowns, where larvae are feeding. Further information on subterranean sod webworm is available at http://extension.usu.edu/insect/ Information compiled and written by Maggie Wolf, USU Extension Salt Lake County. Contact Maggie Wolf at maggiew@ext.usu.edu.
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