Sod Webworms

Sod webworms include at least 20 species within the family Pyralidae. South Carolina turfgrass may be infested by several of the temperate-region sod webworms as well as the tropical sod webworm. These pests feed almost exclusively on grasses. Newly established lawns and sod fields often suffer the worst damage. Damage is much more severe during droughts.

The adult moths are fairly distinctive. Nearly all have a distinct snout-like projection on their head. This is formed by the long labial palpi. The temperate-region sod webworms curl the wings around the body when they are at rest. The tropical sod webworm holds its wings flat. Sod webworm moths are fairly weak fliers. When they are disturbed they will fly a short distance in a zigzag pattern and then settle back into the grass. Most adults are a light brown or tan color. There may be some stripes on the wings.

Sod webworm adults are active at night. The females lay eggs at random on the grass. The eggs hatch in about 10 days and the larvae immediately begin to feed and construct silken tubes in which they live. Sod webworm larvae vary in color from gray or light green to beige or brown. Most larvae have dark spots scattered over the body.

Young larvae may partially skeletonize the grass blades while older larvae remove parts of the blade or clip it off at the base and pull it back into the silken tube. Feeding occurs at night. On cloudy days, the larvae may feed during the day as well. Temperate–region sod webworms may graze small patches of grass to the ground. Tropical sod webworms tend to chew out notches in the grass giving it a ragged appearance. If there is a heavy dew an infested area may appear to be covered with irregular, flat spider webs early in the morning.

Early detection of larval activity is very important in management of sod webworm. If large numbers of adult moths are noticed late in the day the turfgrass should be inspected carefully for larval activity in the next few days. Another indication of larval activity is large numbers of birds working the area in the early morning. A good method for detecting the larvae is to mix one or two fluid ounces of dishwashing detergent per gallon of water and pouring the solution over a 2 ft x 2 ft area. This solution is very irritating to the larvae and they will come to the surface in a short time if present in the grass. Sampling should be done on the edge of suspected damage areas.

Sod webworm larvae are attacked by a wide range of predators, parasites, and diseases. However, these beneficials may not provide enough control to prevent damage to fine turfgrass.

Biorational controls include Bacillus thuringiensis (B.t.) materials (e.g. Dipel and others) and entomopathogenic nematodes. The B.t. materials are most effective against young larvae. Thorough watering of the grass prior to treatment may enhance the effectiveness of the biorational products.

Traditional insecticides are also available for control of sod webworms. All treatments are most effective if applied late in the day. This is because the larvae are active during the night. Always read and follow all label directions when applying any pesticide.

Prepared by Clyde S. Gorsuch, Extension Entomologist/ Professor, Department of Entomology, Soils, and Plant Sciences, Clemson University.

EIIS/TO-21 (New 09/2003).

This information is supplied with the understanding that no discrimination is intended and no endorsement by the Clemson University Cooperative Extension Service is implied. Brand names of pesticides are given as a convenience and are neither an endorsement nor guarantee of the product nor a suggestion that similar products are not effective. Use pesticides only according to the directions on the label. Follow all directions, precautions and restrictions that are listed.

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