From mid-May to October the grass turns brown in patches the size of a saucer in the hottest and driest areas of the lawn. These areas may expand to form large irregular patches. Grass blades are chewed off at the soil level. Silky white tubes are found nestled in the root area. Inside are light-brown or gray worms with black spots, from 1/4 to 3/4 inch long. Called sod webworms, these are the larvae of lawn moths. They can kill an entire lawn in a few days.
Rake out all the dead grass, mow the lawn, and water thoroughly before treating. Damaged lawns may recover rapidly if the insects are controlled early.