I had noticed the gypsy moth caterpillar population building up over the past several years. We've managed to keep them from doing too much damage to our trees by getting rid of the egg masses and killing the caterpillars (mostly squishing them - rubber gloves help!).
The map shows the area of gypsy moth infestation in eastern North America. The gypsy moth caterpillars build over a number of years to the point where they can defoliate entire forests. I remember this happening in the late '80s and the early '90s. The infestation usually isn't fatal, but the trees then have to use up a lot of energy to grow a second set of leaves, and if they're stressed by heat and drought as well, they can die. (So, if you can, do water your trees during drought to keep them healthy.)
After a massive infestation, predator populations rise, and the gypsy moth population collapses. Then we can breathe a sigh of relief for a few years - usually about a decade.
Here's what you can do to control gypsy moth on your property:
• Right now, look at all of your trees, scrape and destroy egg masses to reduce the number of caterpillars during the season. Don't just scrape onto the ground, instead burn them or soak them in kerosene or soapy water. The picture at the right shows you what they look like.For more information: The U.S. Department of Agriculture Forest Service has an informative and well illustrated website about gypsy moth and a list of trees that are most affected.
• Watch for small caterpillars in late spring. A garden hose has enough water pressure to knock them off the leaves and tree trunks and kill them, especially when they are very small.
• Wrap a piece of burlap cloth that's folded in half lengthwise around tree trunks. Caterpillars feed at night and they crawl into the burlap fold to escape the heat during the day. Collect and destroy caterpillars each afternoon. An insecticidal soap spray also kills them. You can squish them if you're not too squeamish, or hand pick and drown them in a bucket of soapy water.
• Trap male moths by hanging pheromone (sex hormone) traps on the trees. These traps act as decoys and prevent male moths from mating with female moths.
• In severe infestations, apply the biological insecticide Bacillus thurigiensis kurtsaki (Btk). This kills the caterpillars, but is only effective when they're quite small. The best time to apply Btk is when the bridal wreath spirea shrub is in bloom.