Spongy Moth

Lymantria dispar

Overview

Spongy moth caterpillars damage fruit trees by feeding on leaves, flowers, and fruit. Generally spongy moths do not require management, but periodically, populations build up to very damaging levels.

Biology

• Spongy moths overwinter as egg masses in woods surrounding orchards and hatch in late April to early May and feed on leaves through June. Spongy moths are seen every year, but usually do not cause problems in apple orchards unless spongy moth populations are very large.
• Small caterpillars can blow into orchards from surrounding woods.
• Large caterpillars can walk into orchards from surrounding woods.
• Caterpillars pupate in early July and adult moths emerge mid - late July. Female moths deposit one egg mass containing 500-1000 eggs.

Monitoring

• Before eggs hatch, scout surrounding woods for spongy moth egg masses.
• From Tight Cluster through Bloom, scout leaves and buds for small, black spongy moth caterpillars. Young trees, in particular, should be monitored.
• Through the end of June, scout apple trees next to spongy moth infested woods for caterpillars walking into orchard.

Management

• Apply a Bt insecticide such as DiPel when caterpillars are 2nd instars, probably during Bloom.
• If large caterpillars migrate into orchards, apply insecticide effective against mature caterpillars such as Delegate or Altacor.