Here is a quick quote from Ohio State University on sod webworms.
The bluegrass, larger and striped sod webworm usually have two generations per year with the summer generation of larvae causing the most damage. The other species have a single generation per year. All the sod webworm larvae spend the winter as a partially grown larva buried several inches deep in the soil. At the approach of warm weather in the spring, the larvae move upward and begin feeding on the lush spring growth of grass. The bluegrass, larger and striped sod webworms finish their feeding in late May to early June. At this time they burrow deeper into the thatch or soil to pupate. After 10 to 14 days, the new adult moths emerge at night to mate and lay eggs. Mated females lay most of their eggs on the second night by randomly dropping the eggs into the turf. The larvae from these eggs feed through July into early August before pupating again. The second generation of adult moths appears in late July through August. Since the turf is usually slowly growing at this time, sod webworm feeding can cause considerable damage. The second generation of larvae feed in September until October but damage is rarely detected because the turf has begun to grow rapidly again.
Figure your control strategy accordingly. Have the customers keep it irrigated in the hot summer and things will not get out of control. We all know how customers are. They probably won't spend the 20 bucks on watering and complain to us that we caused the damage. A little information is your friend. Once the lawn is effected it is possible to mask the damage and regrow grass but it isn't an overnight solution.
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