Squash, flavorful, easy-to-grow annual vegetables, are made up of two species. Winter squash (Cucurbita maxima) includes squashes with hard rinds, such as pumpkin, butternut, Hubbard and acorn, while summer squash (Cucurbita pepo), includes squashes with tender rinds, such as zucchini and crookneck. Both are commonly bothered by a variety of pests, including several types of caterpillars.
Caterpillars are butterflies in the immature, larval stage. The, plump, wormy pests may be as small as 1/2 inch or as large as 3 inches. The appearance of caterpillars varies depending on the type and the source of food. They may be brown, green, black or tan with fuzzy, smooth or spiky skin. The destructive pests initially feed on the flowers and buds of the squash plant, and if left alone, may tunnel into the squash. A variety of caterpillars commonly feast on squash, including pickleworms, squash vine borers, cabbage loopers and melonworms.
Handpicking is tedious, but it is a simple, effective and environmentally safe way to remove caterpillars, especially if your squash patch is small or the infestation is light. Wear gloves because some caterpillars are fuzzy or prickly and can cause an unpleasant skin reaction. You can drop the caterpillars and crush them under your shoe. If that idea doesn't appeal to you, drop them into a bucket of soapy water.
Caterpillars have a number of natural enemies, including big-eyed bugs, damsel bugs, predatory wasps and some types of beetles. The best way to maintain a population of these beneficial insects is avoid using pesticides, which usually kill both good and bad insects. Eliminating caterpillars' natural enemies is often counterproductive and may result in a serious infestation of caterpillars that becomes more difficult to manage.
Bacillus thuringiensis is an environmentally safe, natural bacteria that kills caterpillars within a few days after they feed on the substance. Bacillus thuringiensis is selective and kills only caterpillars. It is nontoxic for people and animals and safe to use on edibles. The product, available at most garden centers, is applied with a hand-held sprayer or a hose-end sprayer. Generally, you mix around 2 teaspoons in 1 gallon of water, mix it, and add it to the sprayer. Check the package because instructions vary.