Zucchini are susceptible to many garden pests. While some pests are relatively harmless, others are quite destructive. Some of the more common bugs that can harm zucchini plants are squash bugs, vine borers, cut worms, aphids, cucumber beetles, and spider mites. Early detection and treatment of these harmful bugs can help save zucchini plants.
Cucumber beetles attack zucchini plants as well as cucumbers. The beetles are yellow-green and have either black stripes or black dots. Aphids are small insects that reproduce rapidly in hot weather. Vine borers are moth larvae that can survive the winter in the soil. Squash bugs are dark gray and about 5/8 inch long when mature. Young squash bugs can be green or light gray and are also capable of surviving the winter in the soil. Cutworms attack seedlings and transplants of all varieties.
Zucchini are susceptible to bug infestation throughout the growing cycle. Gardening Know How.com recommends the plant be treated regularly with insecticide soap as soon as it starts to grow. Cutworms attack young seedlings and transplants, while the other pests attack as the plant matures.
Cutworms can easily destroy young seedlings and transplants when they chew through the stems and eat the leaves. Aphids are not directly harmful to the plants, but they can carry viral diseases from other plants and infect zucchini. Squash bugs and vine borers both survive by sucking the pulp from stems and growing fruit. Infestations from these bugs results in withering leaves and black spots on zucchini squash. Spider mites will discolor leaves, giving them gray or bronze spots. Cucumber beetles feed on the roots and crowns and will cause bacterial wilt on affected zucchini plants.
Insecticide soaps are effective against many pest infestations on zucchini plants. There are also several organic and cultural remedies available that can control harmful pests without the use of chemicals. Lady bugs will naturally help control spider mites and aphids.
Rotate crop plantings every year to discourage repeated pest problems. A Cornell University report on organic and insect disease management suggests planting a "trap crop" around the crops you want to protect. Use the trap crop to attract insects, then spray or treat the trap crop instead of zucchini and other vegetables. The Cornell report also suggests a bird friendly environment will help since they will eat the harmful insects and leave the zucchini alone.