Ask the Gardeners, Q&A
Q Gypsy moth larvae invaded our tree earlier and we tried to spray with Bacillus thuringiensis (BT), not wanting to use chemical pesticides because of birds and other natural predators. Our efforts were not successful for a number of reasons. What can we do? Bacillus thuringiensis must be applied while the caterpillars are still small and two applications may be needed. The young caterpillars ingest this pesticide (harmless to predators) as they feed on leaves. BT is less effective on large caterpillars and totally ineffective on the larvae after they stop feeding and start to pupate.
At the moth stage you should have gypsy moth traps hanging in your trees to lure and catch the male moths as they emerge from their pupae. The females do not fly, so male moths migrate to the females, which are larger and lighter colored. A fertilized female can lay from 100 to 1,000 eggs in a tan felt-covered mass on trees, boards, stone walls, fences, etc. Good fall and winter projects for Scouts, 4-H youngsters, and other groups are to comb areas where moths have been seen, then scrape off and destroy the egg masses. For information on the gypsy moth contact state colleges, extension services, or state departments of environmental conservation. Also the US Government Printing Office, Washington, D.C. 20402. Ask for USDA Home Garden Bulletin No. 225 on Gypsy Moth, Stock No. 001-000-03850-8.