Fall Webworms in Walnut: Identification and Control

Large Silken Webs on Walnut Branches? It's Fall Webworms

Fall webworms (Hyphantria cunea) build large, conspicuous webs at branch tips in late summer, enclosing leaves they feed on. They prefer walnut, pecan, hickory, and fruit trees. While unsightly, they rarely kill healthy trees.

Life Cycle Highlights

• Overwinter as pupae in soil, leaf litter, or old webs.
• Adults emerge May–July; lay eggs on leaf undersides.
• Larvae hatch, spin webs, feed gregariously for ~6 weeks.
• Two generations possible in long summers.

Control Options

Mechanical

• Prune out small, reachable webs.
• Crush webs on small trees.
• Do NOT burn—damages tree.

Biological

• Bacillus thuringiensis (Bt) – spray foliage near webs when larvae are small.
• Encourage predators: birds, wasps, beneficial insects.

Chemical

• Contact sprays (spinosad, bifenthrin, carbaryl) – must penetrate web.
• Systemic soil drenches (imidacloprid, dinotefuran) for tall trees – apply early.

When to Act

• If defoliation exceeds 25% or tree is young/stressed.
• Early detection (small webs) = easier control.

Most mature walnuts tolerate fall webworms without intervention. Focus on tree health and monitoring.