Sod Webworm Control: Lifecycle, Detection & Targeted Treatment

Brown patches in cool-season turf, especially sunny/dry edges? Sod webworms — larvae of small brown moths — chew grass blades and build silk-lined tunnels in thatch.

Detection

• Spring: thin, short patches from early feeding.
• Peak damage: July–August; mimics drought dormancy.
• Confirm: dig in thatch for silk tunnels, or soap drench (2 tbsp dish soap/2 gal water) — tan spotted larvae surface in minutes.

Lifecycle Matters

Eggs laid spring; hatch in 1 week; larva-to-adult in 6–10 weeks; multiple generations/season. Early spring generation causes most damage; later generations hit already-stressed grass.

Control Strategy

1. Water/fertilize regularly to boost recovery.
2. Avoid broad-spectrum insecticides — they kill beneficial predators.
3. Bacillus thuringiensis (Bt) works on young larvae only — timing critical.
4. Labeled insecticide: apply late afternoon (larvae feed at night).
5. Long-term: plant endophyte-enhanced grasses (resistant tall fescue, perennial rye, fine fescue).