Cutworms leave 1 to 2-inch-wide spots of brown grass with the blades chewed evenly along the edges or eaten off at soil level. But because they are surface feeders, they are relatively easy to control.
Cutworms are moth larvae that hide in a lawn's thatch during the day, then come out at night to feed. They chew off grass blades close to the ground. The worms are 1-1/2 to 2 inches long, with fat brown, gray, or black bodies; some are spotted or striped. You may see them curl up in the thatch if you peel back a section of damaged turf.
Because cutworms hide in the thatch layer during the day, controlling thatch can help prevent cutworm infestations. Maintaining your lawn with regular feeding, proper watering, and periodic aerating or dethatching will keep thatch from building up and providing a happy home for cutworms.
Identify the Problem
A large number of birds scratching and pecking at your lawn can indicate a large cutworm population in the grass. Although they are primarily a problem in early and late summer, cutworms can cause harm to lawns all through the growing season. Once they are established in spring, several generations can hatch in one season and damage the lawn before they die out in the fall. Cutworm adults are dark moths with bands or stripes on their forewings. They are often seen fluttering around lights in the summer.
Treat Cutworm Problems
Cutworm damage to mature lawns is usually not severe, but they can damage newly seeded lawns to the point that you need to reseed. If you see cutworm damage in your lawn, apply a control product in the evening when they are most active. You can control cutworms by applying Ortho® Bug-B-Gon® Insect Killer for Lawns. Another option is to spray affected areas with Ortho® Bug-B-Gon® Insect Killer for Lawns & Gardens.