A well-maintained garden is one of the best defenses against damage from caterpillars-the larvae of butterflies and moths. Feed and water plants adequately. Cultivate and weed weekly. Be alert to drooping stems and partly eaten foliage and remove them. By avoiding pesticides, you’ll encourage the presence of caterpillar predators, such as birds, parasitic wasps, lady beetles, and praying mantises.
Promptly after harvesting, burn or trash old leaves and stems; caterpillars can overwinter in them. Dig or rototill your garden in the early spring to expose and destroy pupae. Leaf-eating caterpillars Wearing gloves, handpick large caterpillars and drop them into a pail of warm soapy water or water topped with 1/2 inch of kerosene. For major infestations, spray with Bacillus thuringiensis, a natural control toxic only to caterpillars.
Stem-burrowing caterpillars These borers are invisible and immune to most pesticides. Stunted or yellowing leaves are signs of their presence. Remove squash-vine borers by making a lengthwise knife cut in the stem of a yellowing leaf; discard the pest. Press the split stem together and put some soil over the incision. If damage is widespread, uproot and destroy all affected plants. As a preventive, spray with methoxychlor around the base of squash plants when they begin to produce vines and at 10-day intervals three times thereafter. Wait 1 day before harvest.
Stalk borers, which kill tomato and pepper plants by tunneling in their stems, cannot be controlled by pesticides. Rid your garden of weeds their breeding places. Tree- and fruit-eating caterpillars During winter, look for egg masses on trunks and branches and under loose bark; scrape them off and destroy them. In spring and early summer, trap caterpillars by banding trunks and thick branches with burlap or sticky bands. As the season progresses, replace the sticky bands as necessary and destroy pupae that accumulate in the burlap. Tear out webs of tent caterpillars as soon as they appear.