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Sod Webworm

July 26, 2000

We are getting reports from around the state about sod webworms in turf areas. It is likely that the recent dry weather is allowing these insects to survive and dam-age turf. In damp conditions, microsporidia attack the caterpillars and they die from disease. Look for scattered brownish turf areas, particularly in well-drained locations. Closer observation will reveal that these areas have few grass blades and the area is brown due to the thatch showing. You may be able to see short stubs of green grass blades about 1/16 to 1/8 inch long and small round balls of green feces at the base of the plants.

You can verify sod webworms by using a disclosing solution. Mix 1 teaspoon of 5% pyrethrin (Pyre-none works well) or 1 tablespoon of dishwashing detergent in a gallon of water. Apply this solution evenly over 1 square foot of turf with a watering can or other method. Within 30 to 60 seconds, any caterpillars in the turf will come to the surface. Keep your eye on the area because they commonly go back down into the turf after a few seconds.

Sod webworm larvae are slender caterpillars up to 1 inch long with brown spots. The background color of the body may be gray, tan, or greenish. Two to three larvae per square foot are enough to cause damage. This method also works for black cutworm. If damage or numbers warrant treatment, chlorpyrifos (Dursban), carbaryl (Sevin), and many other insecticides provide effective control. A spray application or lightly watered granular application works best. You want to keep the insecticide on the grass blades and in the thatch where the caterpillars live in order to get control.

Author: Phil Nixon


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