SYMPTOMS: One- to two-inch-wide dead patches with grass blades chewed off just above the thatch line. Usually prevalent in the hottest, driest areas of the lawn. Silky white tubes found nestled in the root area.
INSECT APPEARANCE: Sod webworm larvae are slender, grayish, black spotted caterpillars, approximately 3/4 inch long, and sluggish in their activity. They hide during the day in shelters constructed of bits of grass and debris. The buff-colored moths, which fly in zigzag patterns over the lawn at dusk, have two snout-like projections on their heads.
LIFE CYCLE: Overwintering larvae emerge and begin feeding (at night or on overcast days) in spring. They mature into moths in early summer. Throughout the summer, the moths fly over the grass and drop eggs, which hatch into larvae and repeat the feeding cycle on the grass. There may be as many as three generations per season.
DAMAGE THRESHOLD: Fifteen or more larvae per square foot indicates treatment is necessary.