Karen Miller, Entomologist Specialist
As Master Gardeners we are here to answer questions regarding gardening. This summer we have been bombarded with questions regarding squash bugs. I hope this article will answer some of those questions.
The squash bug (Anasa tristis) is in the Order Heteroptera and Family Coreidae, known as true bugs, the squash bug can cause havoc on all vegetable crops in the cucurbit family, i.e. squash, pumpkin, zucchini, cucumber, melons and some gourds.
The squash bug is common throughout the United States. The adult is a large flattened insect dark gray to dark brown in color, measuring 5/8” long and 1/3” wide. If you look closely you will see that the abdomen protrudes beyond the wings and typically will have alternating orange and brown stripes. The female will lay clusters of yellow to bronze eggs on both the top and bottom of the plant leaf. These eggs will hatch in about two weeks into small, gray nymphs, with long black legs, and will feed on the plant for about a month before reaching the adult stage. During this time the adult female continues laying eggs. The complete cycle from egg to adult is typically completed within six weeks.
Both adults and larvae, or nymphs, of the squash bug, use their sucking mouth parts to suck the plant’s juices. As they feed, they inject a toxic substance that causes the injured tissue to turn black or brown, wilt and die. This process can kill smaller plants while larger plants can recover after all feeding has stopped. When fruit begins to develop this pests, both adult and nymph, often damage it with numerous pinprick-like holes.
As adults this insect is very difficult to kill. Early detection is crucial, as is being diligent in checking your plants for any signs of the insect. Begin watching for the adult squash bug in late spring. This insect overwinters as an adult under rocks, dead leaves and other garden debris. When the temperature begins to warm up, the squash bug will emerge from its winter protection and fly into the garden to feed and mate.
Even though collecting and destroying the bugs and their eggs is the best method of control, there are several others that can help keep them off of your plants. Floating row covers can be placed on seedlings, remove cover only for pollination purposes then recover until the plant is strong enough to tolerate the damage caused by the squash bug. There are varieties of squash plants that are resistant to these insect, you might want to find and experiment with them. One other suggestion is to plant different flowering plants in and around your squash plants to attract natural predators of the squash bug. Predatory flies, spiders, assassin bugs, birds and snakes are also listed as natural predators.
Prevention is the key to controlling the squash bug, be sure to burn, trash, or compost old squash vines. This will eliminate any possible shelter for breeding and over-wintering.
So much for the squash bug, I would also like to touch briefly on one other insect that affects squash, zucchini, pumpkins and gourds. That insect would be the squash vine borer (Melittia cucurbitae).
The adult is a very pretty moth with narrow winged black and red bodies and looks much like a wasp. This moth lays its eggs individually or in small groups on the stem. The eggs are flat, brown ovals. The larvae are white caterpillars with brown heads and tunnel into the base of the vine stem to feed for up to six weeks. This feeding frenzy will cause the entire plant to wilt and die. The larvae will also feed on the fruit of cucumbers, gourds, melons, pumpkins and squash.
This insect hibernates as larvae or pupae in cocoons about an inch below the soil. To detect the presents of this insect look for holes in the lower part of the stem and sawdust-like droppings that are a green to orange-yellow color.
Controlling the squash vine borer is mainly about prevention, also. Planting your squash as early as possible, and harvesting before the vine borer becomes active. By planting early, you may need to cover your plants to protect them from frost. The parasitic wasp is a natural enemy as is the tachinid fly and beneficial nematodes. Use compost tea in your planting beds to promote the number of nematodes in your soil. Also preparing your beds by tilling the soil in the fall and spring before planting will help also.
I hope you have come away with some insight into controlling or preventing problems with squash bugs and the squash vine borer. If you have any questions, you are welcome to call the Ector County Extension office at 432-498-4071 or the Midland County Extension office at 432-686-4700. You can also check out the Permian Basin Master Gardener website at westtexasgardening.org for tips on gardening in West Texas.