A. In the late spring and early summer in Ontario gypsy moths are a major pest of trees and shrubs. In order for you to know how to treat this pest, you need to correctly identify it. The larva is a dark, hairy caterpillar with a double row of five pairs of blue and six pairs of red spots on its back. A buff-coloured egg mass would have been deposited last fall, from which the young emerge in the spring. They move or are blown to suitable host vegetation. They are voracious feeders and can reach up to 7 cm long before they pupate in July. The females moths are flightless and lay egg masses on just about any object, and the cycle begins again.
Treatment: Before the eggs hatch, scrape the egg masses into a container of dish detergent, which will kill the eggs. Once the young have emerged, trap them by tying a band of burlap around the tree trunk, and destroy any caterpillars found inside. You do have to check the burlap daily. There is a chemical control for gypsy moth, and the pesticide is allowed under the new pesticide laws, and that is Bacillus thuringiensis. This should be applied early in the season when the caterpillars are small, no more than 0.5 cm in length.
Zone 5 Director
Master Gardeners of Ontario