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Sod Webworm or lawn moth is one of the most destructive turf pests in Utah. Infestations often damage bluegrass or bluegrass and tall fescue mixes. Sod webworm occasionally attacks tall fescue and bentgrass greens on golf courses.
The sod webworm moths are 1 inch long and whitish-gray or brown in color. The projection from the head, which is formed by a pair of small feeler-like structures arising from the lower lip of the mouth, has also given the name Asnout moths. The immature form of the sod webworm mith is a light brown caterpillar about 1/4 to 3/4 of an inch long. The caterpillar is covered with coarse hairs and may have dark spots on its body. They overwinter in a silken tunnel, becoming active in the spring. Sod webworm caterpillars become full-grown by June. They pupate in the ground and emerge as adult moths in late June or early July.
The caterpillar state feeds on grass blades at night, causing irregular brown patches in the lawn. Many caterpillars working in a lawn cause large dead areas. Do not confuse browned-out patches with diseases or dog injury. Close examination of the damaged area shows a loose silken web containing bits of green droppings leading to a short, silk-lined tunnel in the ground. You can find the worms by breaking apart the damaged areas with your hand. Sod webworm moths are easily disturbed when a person walks across the lawn in the evening. Their peculiar flight pattern is very quick, short, jerky and zig-zag. When resting, the wings are folded closely to the body.
Cutworms are the caterpillars of several species of night-flying moths. The caterpillar feeds on the above-ground plant parts of many grasses and crops. Cutworms are plump, smooth and greasy-looking. They have greenish, brownish, grayish or striped bodies up to 13 inches long. The caterpillars' spring feeding damages plants early in the growing season. They usually hide during the day and feed at night. Adult moths appear in June and July. Females lay about 500 eggs over a two to three week period on the lower grass leaves. A second or third generation may emerge in the summer and early fall. In mid-fall, the caterpillars stop feeding and seek concealed areas in which to spend the winter.
Cutworms feed on grass blades and cutt off plants near the soil surface. Grasses appear ragged and turn brown. Damage is more likely to occur of the lawn borders cropland or large untended fields, because caterpillars wander out of these areas in search of food.
Apply insecticides at the first sign of damage. There is no set time to spray for these insects, so you must watch for their damage.