Sod webworms, the caterpillars of lawn moths including the lucerne moth (Nomophila noctuella), the western lawn moth (Tehama bonifatella) and Sperry's lawn moth (Crambus sperryellus), are night-feeding pests of grasses. These caterpillars hide below the surface of the lawn in silk-lined dens, emerging just long enough to skeletonize or notch grass leaves. Heavy infestations result in brown, patchy lawns, often with bare areas. Bluegrass and bentgrass tend to suffer the most from sod webworms, but any kind of grass can be damaged by these pests. Elimination is a multi-step process, but may result in long-term control of these caterpillars.
Dethatch your lawn with a pull-behind dethatcher or garden rake if the thatch layer is more than 1/2 inch deep. Set your rake to remove as much thatch as possible, or repeatedly rake the lawn with a manual rake until little to no thatch emerges from the grass. Dethatch your lawn at least once a year to prevent a thick layer of thatch, which is attractive to sod webworms, from reforming.
Mix a solution of 2 to 4 tablespoons of dish soap and a gallon of water. Drench 1 square yard of a damaged area of the lawn with the solution. Count the number of sod webworms that emerge during the next 10 minutes. Treat the lawn if more than 15 sod webworms emerge during your test.
Apply Steinerneme carpocapsae nematodes to a lawn that has not had any pesticide applied in the last 60 days. Maximize the potential of your nematodes by applying them in the evening, so they will not be killed by the sun's heat before they've worked into the soil. Use nematodes at the first sign of lawn damage; they are most effective against young caterpillars. Keep the soil moist for at least two weeks after nematode application -- a strong colony can multiply and survive in the soil for years.
Use Bacillus thuringiensis subspecies kurstaki or spinosad on lawns that may be toxic to nematodes due to recent pesticide application. Apply Bt toward dusk or at night so that sod webworms receive a direct dusting as they emerge from their dens; reapply weekly, as needed. Apply spinosad any time of the day, according to package directions since formulations vary. Withhold water from the lawn for at least two days after applying either treatment.
Things You Will Need
- Dethatcher (optional)
- Garden rake (optional)
- Dish soap
- Steinernema carpocapsae (optional)
- Bacillus thuringiensis subspecies kurstaki (optional)
- Spinosad (optional)
- Maintaining a lawn height of about 2 1/2 inches will minimize the visual appearance of light sod webworm damage.
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