Sod webworms

The larvae of small, buff-to-gray lawn moths (snout moths) that fly in a zig-zag pattern just above the turf at dusk and fold their wings tightly when at rest. The caterpillars are gray-to-tan with dark spots, up to about 3/4 inch, and hide by day in silk-lined tunnels in the thatch; their presence is confirmed by green frass pellets in the canopy or by a soap flush bringing larvae to the surface.

Small ragged or closely clipped spots that enlarge and coalesce into irregular brown patches as larvae chew grass blades down to the crown; early injury looks like scattered yellow patches, and on close inspection the turf shows notched, shredded blades, silk-lined burrows in the thatch, and green frass pellets.

Sod webworms are moth larvae with complete metamorphosis. Adults do not damage turf; females scatter eggs over the grass during evening flights, eggs hatch in roughly 7 to 14 days, and the larvae feed and grow through several instars before pupating. There are multiple generations per growing season in warm regions, and northern species overwinter as mature larvae in silk-lined tunnels, resuming feeding and pupating in late spring.

Damage builds in summer, two to three weeks after peaks in moth flight, and is worst on sunny, drought-stressed, and newly established or closely mowed turf. Hot, dry weather favors larval survival, and successive generations can cause expanding injury through late summer.