What’s Bugging Your Garden
Borers and Soil Pests
Borers are either grubs (that become beetles) or caterpillars (the larvae of moths) that feed inside stems. Some borers eat the tissue of swelling buds and fruits; others attack roots or stems. Here are the ones found in most home gardens.
European corn borers are flesh-colored caterpillars up to 1 inch long with rows of round brown spots. The adult moth has a 1 inch wingspan and is yellow-brown with wavy dark bands. Caterpillars first eat holes into the leaves and then bore into the stalks and ears. Bent stalks and casting outside of tiny holes in the stalk indicate that borers are at work. The corn borer is the most destructive corn pest known. The female moth lays about 400 eggs on the underside of corn leaves; the caterpillars hatch in about a week and winter in old stalks left in the garden. It is found almost everywhere in the United States.
European corn borer Photo courtesy OrganicGardenInfo.com
Potato tuberworms are ¾ inch pink or pinkish-white worms with brown heads. They destroy potatoes and also attack eggplant and tomatoes. The adult is a narrow-winged gray-brown moth. The larvae mine the leaves and stems, causing shoots to wilt and die. They also migrate down the stems to the potatoes and burrow in many directions through the flesh. The adult moths lay their eggs one at a time on the underside of the leaves or in the eyes of the potato. After the emerging larvae feed, they pupate in dirt-covered cocoons on the ground. The potato tuberworm is found across the southern part of the United States and as far north as Washington and Colorado.
Potato tuberworms Photo courtesy OrganicGardenInfo.com
Squash vine borers are 1 inch long wrinkled white caterpillars with brown heads. The adult resembles a wasp, with clear copper-green forewings 1 ½ inches across and an orange and black abdomen. The larvae (caterpillars) eat holes in the stems of vine crops. The insect winters in the soil in a black cocoon. When vines start to produce runners, the moth emerges. The females “pastes” eggs on the stems and leaf stalks near the ground. The larvae hatch in about a week and bore into the stems. This pest is especially damaging east of the Rocky Mountains.
Squash vine borer Photo courtesy OrganicGardenInfo.com
Stalk borers are cream-colored 1 to 1 ½ inches long caterpillars with dark brown or purple bands that lighten on the full-grown caterpillar. The adult is a gray moth with a 1 inch wingspan. The caterpillars enter the stems of vegetables and eat out to the inside, while the outer leaves remain green. If they enter near the top and eat downward, the plant wilts. They hatch in early spring, return to the ground in two to four weeks, and change into moths just below the surface of the soil. The female lays more than 2000 eggs on grasses and a few other plants. The stalk borer is fairly widespread east of the Rocky Mountains.
Stalk borer Photo courtesy OrganicGardenInfo.com
Spinach leaf miners are pale green maggots that tunnel inside plant leaves, giving them a blistered appearance, and also attack beets and chard. The adult is a thin, gray ¼ inch long fly. The adult lays up to five oval white eggs on the underside of a leaf. The maggots eat for one to three weeks before dropping from the plant to spin cocoons in the soil. The adult fly emerges two to four weeks later. The spinach leaf miner is found throughout the United States and Canada.
Leaf miner Photo courtesy Missouri Botanical Garden Plant Information
Those marauding plant destroyers that attack from below the soil line are root maggots, the larvae of flies, grubs, root-feeding beetle larvae, wireworms, the larvae of “click” beetles, and cutworms (the last of which was covered under caterpillars). Most destroy vegetables by boring into bulbs, large roots, and stems.
Maggots are the larvae of flies (resembling the common housefly). They are white or yellow, legless, soft wormlike creatures that leave irregular pits in the bulbs and roots of many vegetables.
Cabbage maggots are 1/3 inch long wedge-shaped larvae of the cabbage-root fly. Plants attacked by the cabbage maggot may be stunted and pale, and the roots are often honeycombed with slimy, curving tunnels. The female fly deposits tiny white eggs on the stems of plants near the soil. This pest is found throughout North America and does especially well in cool (below 65 degrees F.) weather.
Cabbage maggots Photo courtesy OrganicGardenInfo.com
Carrot rust flies are strange looking 1/5 inch long shiny green flies with black eyes and yellow heads. Their ugly, yellowish, legless maggots do all the damage by feeding on carrots, celery, fennel, and parsnips. After hatching on the leaves, they work their way down to feed on the roots, causing the leaves of the plants to wilt and turn yellow. If the attack is severe, entire roots can be destroyed. They are commonly found in eastern Canada and the northern United States.
Carrot rust fly Photo courtesy OrganicGardenInfo.com
Onion maggots are the yellow larvae of the onion fly and resemble ordinary houseflies. The leaves of plants attacked by this insect become flabby and faded. The maggot itself tunnels through bulbs and stems, destroying plant tissue. The adult fly lays eggs either in the soil or inside the bulb at the base of the leaves. There are two to three generations per year. The third generation attacks at about harvest time, helping to cause onion-storage rot. The onion maggot affects onions grown in the northern part of the United States.
White grubs and wireworms, both of which can be a nuisance in the garden, are the larvae of the June beetle.
Onion maggots Photo courtesy OrganicGardenInfo.com
White grubs are 1 to 1 ½ inch long “C:-shaped insects with hard brown or black heads. The adults are ½ to ¾ inch long brown beetles. The grubs are most frequently found in soil containing an abundance of humus (organic material). They feed on the roots and underground stems of a number of vegetables. Their life cycle takes three to four years and begins when the female beetle lays eggs in grassy areas. The grubs hatch in three to four weeks and they feed until early fall, when they burrow deep in the soil. For the next two years they feed during the growing season. The third year they remain in the soil as adult beetles, emerging during the fourth summer to begin the cycle all over again. The white grub is particularly troublesome in the south and Midwest.
Wireworms are the larvae of click beetles. They are shiny, yellow to brown insects that are up to 5/8 inch long. They bore into seeds, potato seed pieces, potatoes, and other root crops. Adult click beetles are about ½ inch long, black, and slender. They got their name because when placed on their backs they snap onto their feet with a clicking sound. If wireworms bore into a plant, it comes up but becomes thin and patchy. These pests do great damage to corn as well as potatoes. Each generation requires two to three years to mature. Wireworms are found throughout North America.
Periodically check your vegetable plants from leaves to bottom for any sign of insects damage. If you need to use chemicals try to use the organic products.
Diazinon is an organic phosphate that is especially useful in the soil to control cutworms, grubs, and wireworms.
If you have problems with these creatures practice vegetable rotation in your garden. Before you plant your bed for the new crop, turn over the soil with a shovel or rototiller and then apply diazinon and work thoroughly into the top 3 to 5 inches of soil before planting. Follow directions on package.
The next blog will deal with handling the insect problem by turning the good guys loose.