If caterpillars have infested your trees, don't panic. There are safe ways to deal with the fuzzy critters, and although the appearance of caterpillars and their tents in your trees is unsightly, trees are generally not harmed. A serious infestation of caterpillars can nearly defoliate a tree, but the tree will usually recover and grow new leaves the following spring.
Pull the caterpillar nests out of the trees or prune the affected areas, dropping the caterpillars into a bucket of soapy water. Start early in the spring, as soon as you begin to see evidence of caterpillars. They will be easier to remove and the damage will be less severe.
Spray the leaves with a BTK mixture, a natural biological control for caterpillars that can be found at most garden supply stores, on trees with a serious infestation, or if you can't reach the affected areas. BTK must be eaten by the caterpillars, so be sure to spray BTK when the caterpillars are feeding. Pyrethin spray mixed with insecticidal detergent may be effective as well.
Encourage the caterpillar's natural enemies, such as wasps, yellow jackets and birds. This is the most environmentally sound and least expensive method of dealing with a caterpillar problem.
Remove any wood mulch from around the trees and spread about 2 inches of compost at the base of the tree and work it in to the surface of the soil.
Water the infested trees very heavily for the remainder of the summer. If the weather is dry, let a hose drip for about 2 hours several times a week.
Scrape or pull away any egg masses in the fall. Egg masses will circle small branches, and appear to be a brownish-gray band that hardens and looks similar to Styrofoam. This will help to prevent an infestation the next spring.