Gypsy moths overwinter as egg masses in woods surrounding orchards and hatch in late April to early May and feed on leaves through June. Gypsy moths are seen every year, but usually do not cause problems in apple orchards unless gypsy moth populations are very large.
Small caterpillars can be blown into orchards from surrounding woods.
Large caterpillars can walk into orchards from surrounding woods.
Caterpillars pupate in early July and adult moths emerge mid to late July. Female moths deposit one egg mass containing 500-1000 eggs.
Before eggs hatch, scout surrounding woods for gypsy moth egg masses. Supposedly 250 egg masses per acre can defoliate woods.
From tight cluster through bloom, scout cluster for small, black gypsy moth caterpillars.
Through the end of June, scout apple trees next to gypsy moth infested woods for caterpillars walking into orchard.
Apply a Bt insecticide such as DiPel when caterpillars are 2nd instars, probably during bloom.
If large caterpillars migrate into orchards, apply Delegate or Altacor.