With the dry turf conditions throughout Illinois, watch for sod webworm attack. Sod webworm larvae are usually controlled by disease caused by microsporidia in Illinois. Normally, we have enough rainfall that these organisms are very effective. Any time that we have a protracted dry spell during the growing season, disease is less prevalent, and sod webworms are likely to become numerous enough to be a problem.
Adult moths are present at this time in central Illinois. These moths will be laying eggs over the next two weeks, but all life stages will already be present in the turf as well. With an insect that has three generations per year such as sod webworm, the emergence of generations typically gets very jumbled toward the end of the growing season. Some larvae are slowed in growth because of poor grass quality, cooler temperatures under trees, and various moisture regimes, causing larvae of every size as well as pupae, adults, and eggs to be present constantly at this time of year.
Sod webworms overwinter as larvae, so larvae will be present throughout the fall and are more numerous in dry turf. A long Indian summer increases the likelihood of damage. Dry turf areas should be scouted for sod webworms. Pour an irritant solution of a teaspoon of 5 per cent pyrethrin or a tablespoon of dishwashing detergent in a gallon of water over a square-foot area of turf. Two to three of the slender, brown-spotted sod webworm caterpillars per square foot are enough to cause damage. Once detected, several insecticides are effective control agents.