What are cutworm?

Cutworms are large, plump, dull coloured grayish, green and brown larvae which viciously chew on grass plants. They live on the soil surface or in the thatch layer. During the day they burrow into vertical holes to hide. When nightfall arrives they emerge from their burrowed hole and feed at the rim of the hole. Stems, leaves and roots of the grass plants may be injured leaving yellowish brown dead patches with a hollow hole in the middle of the circle. The damage looks quite similar to symptoms of dryness and many homeowners mistakenly assume that the lawn requires only water to restore the lush appearance. Another symptom to watch for is birds- Starlings have a keen ability to locate cutworm larvae. When these birds return frequently to an area cutworm larvae may be present.

CUTWORM LIFE CYCLE

The adult cutworm appears in the spring as a grayish/brown moth with a 1 to 1 ½" wing span. Adult cutworms do not damage lawns. They lay their eggs in the spring during the night leaving them on grass blades. Larvae emerge and begin feeding as early as June with damage appearing in June/July. Cutworms actually feed at night on grass blades which they chew off close to the base of the plant. Dead patches of grass begin to appear and may be pulled away easily by hand.

What are sod webworms (Parapediasia)?

Sod webworm adults are small tan moths ½ to ¾" long. The adults are frequently seen darting across the lawn, especially when disturbed. The moths do not harm the lawn. The immature or larvae stage of the sod webworm are as long as ¾" and are dirty white or tan coloured and frequently have rows of dark spots along their back. As with cutworm damage, their damage appears similar to that of dryness. As larvae they construct tunnels or burrows throughout the thatch layer, sometimes extending into the soil. The name webworm is derived from the insect's habit of lining its tunnel with a silk like material they produce.

Sod webworm life cycle. 

The adult moths emerge from the lawn in May or June flying mainly during the evening hours laying eggs randomly throughout the lawn. The larvae emerge from the egg and begin feeding immediately. Damage is caused by larvae chewing off grass stems and leaves while feeding during the summer and into early fall. The dead patches of grass pull away easily in clumps revealing masses of silk with the green excrement pellets left by larvae.

How can I treat for cutworm and sod webworm? 

The best time to treat cutworm and sod webworm is when they are very young in June/July before severe damage occurs. By early fall they begin to transform into adults. In the adult stage they are very difficult to control. If you notice suspicious brown patches starting to appear in the lawn, DO NOT HESITATE! Call your local Weed Man Professional for a free healthy lawn analysis. Weed Man can verify the presence of a potentially damaging infestation, discuss preventative measures and recommend treatment if required. Consult your local Weed Man Professional to discuss all options with respect to dealing with insects in your lawn.