SYMPTOMS: As with armyworms, cutworms leave small, 1- to 2-inch-wide patches of brown grass in newly seeded and established lawns; the plants are eaten off at soil level.
INSECT APPEARANCE: The larvae of cutworms are plump, smooth, and almost always curl up when disturbed. They can be various colors but are most often gray, brown, or black; some are spotted or striped. They often grow to 2 inches long. The moths are dark and fly at night.
LIFE CYCLE: Moths lay their eggs in late summer, and after hatching, cutworm larvae over winter in trash and clumps of grass. Larvae resume feeding early in spring (and only at night). They mature into moths in July or August.
DAMAGE THRESHOLD: Use the pyrethrum test (listed below), to determine how pervasive these insects are. If you find more than 10 larvae per square foot, it's time to act. Cutworms don't seriously damage grass unless there is a severe infestation. More damage may be done by birds scratching at the turf to feed on the larvae.
PYRETHRUM TEST: Other insects, such as sod webworms, can be driven to the surface of the soil by drenching a patch of lawn with pyrethrum, a natural pesticide. Mix 1 tablespoon of a 1- to 2-percent pyrethrum pesticide in 1 gallon of water. Mark off about 1 square yard, and apply the entire gallon mixture as evenly as possible using a sprinkling can. If those insects are present, within a few minutes they will rise to the surface of the lawn, where you can then spot and identify them.
CONTROL: Bacillus thuringiensis, carbaryl, chlorpyrifos, diazinon, neem, pyrethrum.