Like anywhere else, Iowa has its share of vegetable garden pests. Vegetable pests that are especially prevalent in Iowa gardens are the tomato hornworm, squash bug and vine borer, and rootworm, according to the Iowa State University Entomology Department. Some vegetable garden pests do little damage and are mostly a nuisance, while others can decimate your garden and wipe out your vegetable crops. Identifying these vegetable insects properly is the first step to taking the actions necessary for getting rid of harmful garden pests.
The tomato hornworm is a common vegetable garden pest in Iowa, feeding on the tomato plant leaves and fruits. The tomato hornworm also attacks eggplants, peppers and potatoes. This garden insect is 4 to 5 inches long and bright green or red, depending on the exact species. The tomato hornworm is recognizable by its hornlike hook. These pests can easily and rapidly defoliate the vegetable plant and damage the fruits. Tomato hornworms feed on the vegetable garden plants throughout the spring and summer, and then they tunnel into the soil and pupate during winter. They emerge the next summer in adult form as the five-spotted hawk moth. Pick the tomato hornworms off the plants by hand, or apply the biological insecticide Bacillus thuringiensis, according to the instructions on the label.
The squash bug, also known as the stink bug, is often found in Iowa vegetable gardens, feeding on all fruits of the squash and pumpkin family. The adult squash bugs appear when the plant vines begin to grow along the ground. They're about 1 inch long, grayish-black or brownish, elongated and often with a shield-shaped shell. In late spring through mid-summer, the squash bugs lay their large, reddish to brownish eggs in clusters on the undersides of the leaves. The green nymphs feed on the plant's sap in clusters for about four to six weeks until they become adults. The adult squash bugs also feed on the unripe fruits in late summer before moving to protected locations for the winter.
To get rid of squash bugs, spray your vegetable plants with permethrin or an insecticidal soap according to the instructions on the label. Avoid spraying plants while they're blooming unless absolutely necessary, because these insecticides can kill beneficial honey bees too.
Squash Vine Borer
Another vegetable garden pest in Iowa is the squash vine borer, which bore into squash and pumpkin plant stems, causing the vines to wilt. Squash vine borers are fat, white caterpillars found near the stems, close to the soil surface, from June until August. The adult is a moth that looks like a wasp, flying from plant to plant during the daytime from early to mid-June to lay its eggs on the outer stems. Apply a residual insecticide, such as permethrin, bifenthrin, spinosad or carbaryl, to the base of the squash and pumpkin plants when the adult moths are still flying around in early summer. If the vegetable plants are already infested with the borer larvae, the insecticides won't be effective and you'll need to remove the borers from the stems by hand.
Rootworms are common garden pests in Iowa, especially the northern and western corn rootworms. These rootworms feed on the roots of Iowa corn during spring and early summer, and then move on to nearby gardens to feed on vegetables and flowers. Rootworms are beetle larvae that pupate in mid-summer, before the adult beetles migrate to the vegetable gardens. Rootworm beetles are frequent pests of melons and pumpkins, feeding on fruit rinds in late summer through autumn. There is no effective insecticide or chemical treatment to get rid of rootworm beetles on vegetables or flowers.