Select good transplants. Inspect plants carefully before you buy them. Whiteflies, mites, aphids, and leafminers often overwinter in the greenhouse and can easily hitch a ride to your garden on transplants. So, shop with reputable dealers and be wary of discounted seeds or plants. Plant early enough to get a crop in before insect levels begin building in the summer and peak in the fall.
Commercial traps can help with Japanese beetles, but homemade traps can be effective, too.
If you put an 18-inch square piece of an old shingle or cardboard under squash plants, squash bugs will congregate under it for protection from the heat of the day. Lift the board and smash them with a hoe. Mulching squash only gives bugs a place to hide. Bacillus thuringiensis, a biological control for caterpillars, is especially effective on cole crops. It is non-toxic to everything else and is readily available at most garden centers.