Large gypsy moth outbreaks are due in part to a warm, dry spring. Having a spring that is cool and wet, there are 2 diseases (a virus and a fungus) that help to keep gypsy moth (a non-native pest) in check.
It is important to count up and survey how many egg masses you have on your property in order to determine how bad it will be next year. Each egg mass contains 400-600 eggs. Do not just scrap off egg masses thinking you have killed them. They will hatch on the ground next spring and work their way up the tree to feed in May.
Gypsy moth are best controlled in very early May (just as leaves emerge on forest trees) when they are small and just hatched from eggs. Aerial spraying of a natural bacterium (Bacillus thuringiensis or Bt) will kill young, small caterpillars, without any harm to other wildlife or humans. Once the caterpillars get big, Bt does not work on them and other registered pesticides can be used, but major damage occurs to tree canopies when they get large.
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