Plant Problem Diagnostic
Sod Webworms in Lawns
The short answer
Sod webworms are the larvae (caterpillars) of small lawn moths that chew grass blades and stems just above the crown, creating small brown patches of closely clipped turf and exposed thatch that can merge into larger irregular dead areas.
The tell-tale signs are notched or chewed blades, silk-lined tunnels in the thatch, and moist green fecal pellets (frass); the dull-colored adult moths give themselves away with a jerky zigzag flight over the turf at dusk.
Because lawn diseases and drought produce similar brown patches, confirm larvae are actually present before treating: drench a suspect patch with a soap-and-water solution and watch for caterpillars to surface.
Healthy, well-maintained lawns tolerate and recover from webworm feeding, so if a soap flush turns up no larvae the problem is something else and an insecticide will not help; when control is warranted, Extension names Bacillus thuringiensis (Bt) and insect-parasitic nematodes as least-toxic options.
How to identify sod webworm damage
Damage appears in midsummer as small brown patches where grass blades are missing rather than simply dead, often the size of a baseball or smaller, which can coalesce into larger irregular areas.
Look closely for grass blades that appear notched or chewed after feeding, and for silk-lined tubes (tunnels) where the larvae hide down in the thatch.
A reliable sign of fresh, active feeding is the presence of moist, fresh, green fecal pellets in the thatch.
Watch for the moths at dusk
The adults are dull-colored moths with a roughly three-quarter to one-inch wingspan and a snout-like projection from the front of the head.
At rest they often face downward on a grass stem and wrap their wings around the body, then fly in a distinctive jerky, zigzag pattern low over the turf at dusk. Seeing this evening flight is a cue to start scouting for larvae.
Confirm with a soap flush
Larvae can be brought to the surface by drenching an infested area with a soap solution and watching for caterpillars to wriggle up out of the thatch within a few minutes.
- 1Mix the drench — Combine about 1 ounce of liquid dishwashing soap with 3 gallons of water (per University of Minnesota Extension).
- 2Apply to a suspect patch — Pour it evenly over a small area at the edge of the browning turf where damage meets healthy grass.
- 3Watch and count — Look for larvae to come to the surface within about 2 to 10 minutes.
Distinguish from disease and drought, then decide on control
Several lawn diseases cause brown patches that resemble webworm injury, and feeding damage often goes unnoticed during drought; if a soap flush and inspection turn up no larvae or feeding, the cause is something else and an insecticide will not provide control.
Because healthy lawns tolerate and recover from feeding, sound watering and mowing are the first line of defense. When treatment is justified, Extension lists Bacillus thuringiensis (Bt) formulations and insect-parasitic (Steinernema) nematodes as biological options, and notes insecticides work best applied in late afternoon or early evening when larvae are active.
⚠ No larvae in the soap flush means no webworm problem to spray for. Reach for cultural fixes and re-diagnose rather than applying insecticide to a disease or drought patch.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- Penn State Extension — Sod Webworms in Home Lawns — Adult moths recognized by jerky zigzag flight over turf at dusk; at rest they face downward and wrap wings around the abdomen; fresh feeding indicated by moist green fecal pellets in thatch; Bt formulations and Steinernema nematodes are labeled/biological controls.
- University of Minnesota Extension — Sod Webworms — Damaged leaves may appear notched; larvae reside in silk-lined tubes in thatch; drench turf with 1 ounce liquid dish soap in 3 gallons water and watch for larvae to surface within 2 to 10 minutes; if no larvae are found the problem is due to other agents and insecticide will not control it.
- UC IPM — Lawn Moths and Sod Webworms — Damage appears as small circular quarter-size areas of closely clipped grass and exposed brown thatch that merge into larger irregular dead areas; healthy lawns tolerate feeding.