Sod webworm damage

Sod webworms are the larvae of small moths that fly in a distinctive zigzag pattern close to the lawn surface at dusk. Adults do not damage grass -- they are simply the indicator that larvae are present or will soon be. The caterpillars that hatch from their eggs feed on grass blades at the soil.

—- title: "Sod webworm damage" slug: lawn-sod-webworm hub: lawn category: "Lawn guide" description: "Identify and treat sod webworm damage on cool-season and warm-season lawns: adult moth flights, larval feeding signs, soap flush diagnosis, and treatment options." date: 2026-06-10 updated: 2026-06-10 author: "Thomas A." reading_time: 8 —-

Sod webworms are the larvae of small moths that fly in a distinctive zigzag pattern close to the lawn surface at dusk. Adults do not damage grass — they are simply the indicator that larvae are present or will soon be. The caterpillars that hatch from their eggs feed on grass blades at the soil surface, creating ragged, irregular patches that progress from small to large over 3—4 weeks.

Species overview

Per Cornell Cooperative Extension, numerous sod webworm species affect lawns in the United States. The most common include:

• Larger sod webworm (Pediasia trisecta) — widespread in the Midwest
• Bluegrass webworm (Parapediasia teterrella) — northeast and north-central states
• Tropical sod webworm (Herpetogramma phaeopteralis) — Florida and Gulf Coast, on warm-season grasses

Per UF IFAS Extension, the tropical sod webworm is a significant pest of St. Augustine grass, bermuda grass, and zoysia in Florida and the Gulf South — distinct from the temperate species affecting cool-season northern lawns.

Life cycle

Per Rutgers NJAES, most temperate sod webworm species have 2 generations per year in the mid-Atlantic and northeast:

• Adults fly in a zigzag pattern low over the lawn at dusk in June and late July—August, dropping eggs into the grass canopy
• Eggs hatch in 7—10 days; young larvae feed on leaf surfaces initially
• Mature larvae feed at the soil surface at night, cutting grass blades close to the thatch line
• Larvae overwinter in the soil and thatch as partially grown caterpillars, resuming feeding in spring
• Pupation in May—June; adults emerge June for first generation

Identifying adults

Per Cornell Cooperative Extension, adult sod webworm moths are:

• Small (0.75—1 inch wingspan), straw-colored to brown
• Distinctive resting posture: wings wrap tightly around the body, forming a cigar shape
• Fly low in a zigzag pattern over lawns at dusk
• Disturb them by walking through the lawn in the evening — they flush up and resettle quickly

Seeing adult moths is not a treatment trigger — it is a warning to monitor for larvae and check for damage.

Damage symptoms

Per Penn State Extension:

• Irregular, ragged-edged brown patches developing from July through September
• Close inspection reveals blades cut off just above the thatch line, not at the crown
• Green fecal pellets (frass) are visible in thatch in affected areas
• Silk tunnels in thatch layer created by larvae — visible when the thatch is parted
• Birds feeding in the area are an indicator

Confirmation: soap flush test

Per Rutgers NJAES, mix 2 tablespoons of dish soap in 2 gallons of water. Pour over 1 square foot at the margin of damaged turf. Sod webworm larvae emerge within 2 minutes. Count larvae per square foot to assess population:

• Under 5 per square foot: Low pressure; treatment optional if turf is healthy
• 5—15 per square foot: Moderate; treatment advisable
• Over 15 per square foot: High; treatment warranted

Treatment

Per Rutgers NJAES and Cornell Cooperative Extension:

Timing: Apply insecticides in late afternoon or early evening when larvae are actively feeding at the surface. Mow before treating to remove excess leaf material. Do not irrigate within 24 hours of contact insecticide application.

Chemical options:

Per Penn State Extension, thatch over 0.5 inches reduces insecticide penetration to the soil surface. If thatch is excessive, dethatching before treatment improves efficacy.

Recovery

Per Cornell Cooperative Extension, lightly damaged lawns (crowns intact) often recover without reseeding when pressure is eliminated, temperatures cool, and moisture is adequate. Heavily damaged areas should be overseeded in early September with endophyte-enhanced ryegrass or tall fescue — endophytic cultivars have natural chemical resistance to many surface-feeding insects.

Tropical sod webworm (warm-season lawns)

Per UF IFAS Extension, the tropical sod webworm is a year-round pest in south Florida and a seasonal pest in the Gulf Coast states. It produces multiple overlapping generations per year, causing recurrent damage from June through October. Symptoms and management are similar to temperate species, but the rapid generation time means monitoring must be more frequent. Bifenthrin and chlorantraniliprole are the primary chemical options; spinosad is the primary organic option.

Common problems

Frequently asked questions

How do I tell sod webworm damage from armyworm damage? Per NC State TurfFiles, both create irregular brown patches from leaf feeding. Armyworm damage is often more rapid — progressing across a lawn in 3—5 days — and armyworms are larger caterpillars. Sod webworms are smaller and damage progresses more slowly. The soap flush identifies both.

Does sod webworm damage kill the lawn permanently? Per Cornell Cooperative Extension, sod webworm feeding removes leaf blades but typically leaves crowns and roots intact. Stressed or drought-weakened turf is more likely to suffer permanent damage. Well-maintained, adequately watered lawns often recover from light to moderate infestations without intervention.

Are there natural predators of sod webworms? Yes. Per Penn State Extension, numerous natural enemies attack sod webworm larvae and eggs, including parasitic wasps, ground beetles, and birds. Reducing broad-spectrum insecticide use preserves these beneficial organisms and is part of a long-term integrated management approach.

Should I apply preventive insecticide for sod webworms? Per Rutgers NJAES, preventive insecticide for sod webworm is not standard practice in home lawns. Monitor for adult flight (dusk walking/observing), confirm larvae with the soap flush test, and treat only when thresholds are exceeded. Routine preventive applications create unnecessary pesticide exposure and kill beneficial insects.

Recommended gear: Best BT Spray: Bacillus thuringiensis for Caterpillar Control — our buyer's guide covering picks for every budget, ranked by Extension publication consensus and personal use.

Sources

1. Cornell Cooperative Extension — Sod Webworm Management
2. Rutgers NJAES — Turfgrass Insects
3. UF IFAS Extension — Tropical Sod Webworm
4. Penn State Extension — Lawn Insect Pests