The insect pest Gypsy Moth feeds on hundreds of varieties of trees and shrubs. The moth prefers the oak as a host tree - such as New Jersey’s state tree, Northern red oak.
The Gypsy Moth, originally from Europe, was introduced to Massachusetts in 1869 by a French botanist trying to develop the silkworm industry. Once the insects escaped from his laboratory, they colonized and spread. Currently gypsy moths populate 19 states. Without intervention this pest spreads at a rate of about 13 miles per year.
To control gypsy moths a property owner should monitor populations, maintain tree health, remove and destroy egg masses, and trap larvae by banding trees with burlap. Heavy infestation may require treatment with insecticide such as Bt (Bacillus thuringiensis) - a naturally occurring bacteria. Bt is often recommended because it only affects the caterpillar stage of moths and butterflies. Spray the tree’s leaves with Bt from late April to early May when caterpillars first hatch and are less than 5/8” long. Bt does not work on older caterpillars or other moth life stages. Some Bt brand names are: Dipel , Thuricide, and Caterpillar Attack. Read all instructions before applying pesticides. Homeowners should consider hiring a NJ Certified Tree Expert to develop a control plan to protect their tree resource.
If a healthy tree is defoliated, the tree may re-leaf during the summer, but with smaller leaves. This stress to the tree makes it more susceptible to borers, fungus, and drought. A healthy tree may be able to survive one or two defoliations. A stressed tree may partially or totally die from defoliation and the impact may not be seen for many years.
In 1981, New Jersey suffered the worst gypsy moth defoliation of 800,000 acres. From aerial surveys, New Jersey foresters have determined that populations are on the rise again. From 42,000 acres defoliated in 2005, the infestation has risen to over 127,000 acres in 2006, and 324,000 in 2007.