Diagnosing Sod Webworm Damage in a New UK Lawn

A homeowner in West Sussex, UK, moved into a new build on former nursery land with clay soil. The lawn declined from a small dry patch; blackbirds pull up grass tufts. They haven't watered due to restrictions.

Identification: Sod Webworm

• Adult moth: ½ inch, tan/buff, wings held tubelike at rest; flies in dipping zigzag.
• Caterpillar: gray/greenish, up to 1 inch, slender, brown spots; emerges at night from silk-lined thatch tunnels to eat blades to the crown.
• Signs: irregular brown areas (thatch exposed), green 1/8-inch frass at base, damage during dry periods.
• Birds digging for caterpillars are actually helping.

Control

• Chemical insecticides are effective.
• After control, irrigate to help crowns regrow leaves.

Resources

• OSU Sod Webworm
• KSU Sod Webworm
• UT Extension
• Montana IPM

Even with water restrictions, targeted treatment and subsequent irrigation (when allowed) can restore the lawn.