What’s Bugging Your Garden: Borers and Soil Pests

Borers attack roots, while others eat buds and fruits

Reader Contribution by Karen Newcomb
Updated on July 7, 2021
article image
by Flickr/Alabama Extension/Janet Guynn
Squash vine borer.

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.

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.

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.

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.

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.

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