Sod webworms are one of the most frustrating lawn pests homeowners encounter during warmer months. These small caterpillars feed on grass blades and can quickly create brown, thinning patches across an otherwise healthy lawn.
Because the damage often looks similar to drought stress or lawn disease, sod webworms frequently go unnoticed until the infestation becomes severe. With proper identification and the right treatment, however, homeowners can stop them before they destroy large areas of turf.
Sod webworms are the larval stage of lawn moths. The adult moths themselves do not damage grass — but their caterpillar-like larvae feed heavily on turfgrass, chewing blades down to the crown and leaving behind ragged, thinning turf.
Sod webworm larvae characteristics:
- Small and worm-like — usually less than 1 inch long
- Gray, green, or tan in color with small dark spots
- Hide in the thatch layer during daylight hours
- Most active at night, feeding on grass blades after dark
- May produce fine silk webbing near the soil surface
You may notice the adult moths first — they fly in a low, zigzag pattern over the lawn at dusk. The moths themselves are harmless, but their presence means eggs and larvae are likely already in your turf.
Damage from sod webworms often starts small but can spread quickly during hot, dry summer weather. Lawns may initially appear drought-stressed before patches begin dying outright.
Common symptoms to watch for:
- Brown or thinning patches of grass that appear irregularly shaped
- Grass blades that look chewed, ragged, or stripped near the surface
- Small silk webbing visible near the soil level on close inspection
- Increased bird activity — birds actively feeding on the lawn are a strong sign
- Lawn moths flying in low zigzag patterns over the grass at dusk
- Damage that does not improve with watering or fertilizer
Sod webworm damage is typically most severe in sunny areas with thin or drought-stressed turf. If you see moth activity in the evening, inspect closely for larval feeding the following morning.
Before treating, confirm sod webworms are the cause. The easiest method is the soap flush test, which forces larvae to the surface for easy identification.
Soap flush test — step by step:
- Mix 1–2 tablespoons of dish soap into one gallon of water
- Pour the soapy solution slowly over a 1-square-foot section of damaged turf
- Wait 5–10 minutes and watch the surface closely
- Sod webworm larvae will emerge from the thatch and crawl to the top
Finding multiple larvae per square foot confirms an active infestation that warrants treatment. A handful of larvae in a single test area indicates it is time to act before damage spreads further.
Step 1
Mow & Dethatch
Reduce thatch to remove larval hiding places. Mow the lawn before applying insecticide to help product penetrate the turf layer more effectively.
Step 2
Apply Insecticide
Use bifenthrin, carbaryl, or Bt products. Apply in the late afternoon or early evening when larvae are most active and closest to the surface.
Step 3
Water & Monitor
Water lightly after application as directed. Re-inspect treated areas after 10–14 days to confirm larvae are controlled before patches recover.
For organic options, Bacillus thuringiensis (Bt) products are highly effective against young larvae and safe for beneficial insects. Beneficial nematodes can also help suppress populations when applied to moist soil in the evening.
Recommended products for sod webworm control:
Healthy, thick turf is far more resistant to sod webworm damage than thin or stressed grass. Prevention starts with consistent lawn care throughout the growing season.
Key prevention practices:
- Keep grass properly fertilized — strong turf resists and recovers from pest damage
- Reduce excess thatch to remove the moist, protected environment larvae need
- Aerate compacted soil to improve root health and turf density
- Avoid cutting grass too short — mow at the upper end of recommended height
- Water deeply 1–2 times per week during dry periods to reduce drought stress
- Monitor lawns weekly in June through August — look for moth activity at dusk
- Inspect suspect areas using the soap flush test before damage spreads
Final Thoughts
Sod webworms can quickly damage a lawn during hot summer months, especially when grass is already stressed by drought or poor growing conditions. Because damage often looks like a watering issue, early identification is the most important step.
With consistent lawn care, regular monitoring for moth activity, and targeted treatment when larvae are confirmed, homeowners can stop infestations before serious damage occurs. A thick, healthy lawn is always the best long-term defense against sod webworms and most other lawn pests.
