WSU Extension

Hortsense

Lawn and Turf : Sod webworm
(revision date: 3/10/2017)


Biology
Sod webworms are the larval stage of lawn moths. The adults are slender, grayish-white to tan moths with a wingspan of approximately 1". They typically fly at dusk in erratic patterns over the lawn and are attracted to lights. Mature caterpillars are 3/4"-1" long and grayish or greenish in color with brown spots. They feed at night, hiding during the day in tunnels of grass and debris tied together with webbing. Damage consists of leaf blades chewed off at the base of the plants. Grass shoots may die back, resulting in irregular brown spots in the lawn. Caterpillars and their droppings (frass) are usually present at the base of plants (in the thatch layer) in the damaged areas. Sod webworms are primarily a concern in eastern Washington, although they can be a problem in western Washington in periods of drought. Grasses which produce more thatch are more susceptible to damage.
Management Options

Non-Chemical Management
  • Natural enemies including birds, ants, spiders, and predacious ground beetles help keep sod webworm populations below damaging levels. When possible, avoid use of broad-spectrum insecticides which kill beneficial insects.
  • Maintain thatch at proper levels. Thick thatch encourages sod webworms and enhances their damage.
Select non-chemical management options as your first choice!

Chemical Management

Insecticides are recommended for reducing the larval stage. They may not reduce the number of moths flying around. Only apply products at the larval stage for reduction in populations. Mow or remove weed flowers before applying.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.
  • Bull's-Eye Bioinsecticide
    Active ingredient: spinosad (spinosyn A+D)  |  EPA reg no: 62719-314-56872
  • ferti-lome Borer, Bagworm, Tent Caterpillar & Leafminer Spray
    Active ingredient: spinosad (spinosyn A+D)  |  EPA reg no: 62719-314-7401
  • Monterey Garden Insect Spray [Organic]
    Active ingredient: spinosad (spinosyn A+D)  |  EPA reg no: 62719-314-54705
  • This list may not include all products registered for this use.
Images
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Caption: Sod webworm
Photo by: R.D. Akre