Sod Worm

Symptoms and Signs

There are several species of caterpillars called sod webworms that can be highly destructive pests. They may also become important pests of grass covered parks, cemeteries, golf courses. They have even been noted to cause damage in small grain crops such as corn, wheat and oats. Damage to grass is caused by the feeding of the larval or "worm" stage. The adult moth does not cause damage to turf, other plants or clothing.

The damage caused by sod webworms may first appear in early spring. The damage shows up as small dead patches of grass among the normally growing grass. The summer generation may cause general turf thinning or even irregular dead patches in late June into early August. Sod webworms prefer sunny areas and the larvae are often found on south facing, steep slopes and banks, where it is hot and dry. Heavily shaded turf is seldom attacked by the larvae.

The most severe damage usually shows up in July and August when the temperature is hot and the grass is not growing vigorously. In fact, most sod webworm damage is mistaken for heat and drought stress.

The surest way to tell if you have sod webworms is to find a suspected area of infestation (brown patches). Get down on your hands and knees, take your two index fingers and part the grass blades in the area between dead and live grass and look for an area with small green pellets. The pellets, called frass, are the excrement of the larvae and indicate that a larva is close by. Sod webworm adults are about 3/4-inch long, cigar-shaped and buff-colored moths. They typically roll their wings around the body when resting on a grass blade. Two small snout-like projections are visible at the front of the head.

Management:

Control should only be directed towards the feeding larvae, not the flying adults. Since drought stress and turf diseases can cause thinning similar to sod webworm damage, be sure to check the turf for frass or use the soap disclosing flush to determine that larvae are present. Use Fertilizer and Water - Damage can often be outgrown if water is continually available. Considerable damage may occur if irrigation is not possible during periods of drought or close mowing is used.

Most sod webworms are easily controlled if the pesticides are ingested when the larvae feed shortly after dark. Therefore, best control is achieved by spraying in the late afternoon. Late fall or early spring applications are often not effective because many larvae are hiding in deeper soil chambers.