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Bluegrass Webworm

July 7, 1999

Bluegrass webworms have been noticed in large numbers in scattered areas of central Illinois. This webworm is most noticeable on golf courses because of its ability to damage bentgrass, as well as bluegrass, rye, and fine fescues. Damage appears on bentgrass greens and fairways as roundish brown areas several inches in diameter. Damage is not usually as obvious on the other hosts, probably due to higher mowing. The adult moths are smaller than other webworms; they are only about 1/2 inch long. The wings of these tan moths do not curl into a tube shape when they are at rest as the wings of sod webworms do.

Scout for bluegrass webworms as you would for other turf caterpillars. Mix a teaspoon of 5 percent pyrethrin or a tablespoon of dishwashing detergent in a gallon of water and distribute it over a square foot of turf with a watering can or sprayer. Larvae should appear on the turf surface in about 30 seconds. Keep your eye on the area because caterpillars burrow back into the thatch after a short time. Bluegrass webworms are slender, light-colored caterpillars that may appear greenish because their food can be seen in their guts. Unlike greater sod webworms, they are not covered with brown spots. Three or more caterpillars per square foot are likely to cause damage.

Bluegrass webworms are easily controlled with a variety of insecticides, including bifenthrin (Talstar), carbaryl (Sevin), chlorpyrifos (Dursban), halofenozide (Mach 2), spinosad (Conserve), and trichlorfon (Dylox, Proxol). These insecticides are also used to control cutworms, so greens treated for cutworms are unlikely to get bluegrass webworms. Webworms are also controlled with entomophagous nematodes including Steinernema carpocapsae and Heterorhabditis bacteriophora.

Author: Phil Nixon Roscoe Randell


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