Guide to Corn Pests, Insects, and Bugs

Many species of pests attack corn and cornstalks. To learn to recognize them, begin by looking at which part of the plant they eat.

Seed Corn

When corn seeds fail to sprout or only send up weak seedlings, the seed corn maggot is the most likely culprit.

Their eggs, laid in the soil, hatch in early spring. These eggs can thrive at temperatures as low as 40°F (4.4°C ). The larvae grow to 1/4 in. (6.3 mm) in length, with pointed heads, tough, yellowish-white skin, and no legs.

After eating, the larvae form pupae, which are a reddish-brown color. In two weeks, the adult form, small flies, emerge and are ready to lay more eggs.

Seedlings

You can identify the killer of corn seedlings using their modus operandi.

Cutworms and grasshoppers, for instance, slice the stalk off near the ground. Billbugs and stink bugs eat the heart of the plant, stunting its growth enough to render it useless. Sugarcane beetles chew cavities into seedlings, just below the surface of the soil.

Southern corn leaf beetles carve notches into seedlings’ leaves in May. These are brown or gray, about 3/16 in. (4.7 mm) long, and have a dusty appearance when covered with dirt.

Roots

Asiatic beetles feed on root hairs, weakening the plant. Roots are also a favorite of corn flea beetles in their larval stages. Rot sets in from fungus if the soil is below 55°F (12.7°C ) at planting time. Aphids are small green insects that feast on corn roots in the spring and overwinter in ants’ nests during the winter. So, it’s best to plow these nests under in winter. 

Adult spotted cucumber beetles lay their eggs near corn roots in the fall. In the spring the yellowish grubs, or southern corn rootworms, hatch and eat the roots, causing the plants to blow over in the breeze. Rotating crops and plowing corn stalks under after the harvest will help to prevent this insect from making a pest of itself. 

Stalks and Leaves

Many pests see corn plants as a big, luscious salad. Adult corn flea beetles are brown and the size of a pinhead. They eat the stalks of corn plants that are growing slowly due to poor nutrition. 

The corn leaf aphid is gray or bluish-green with black trim, round, and also about the size of a pinhead. Unlike other species, the female, instead of laying eggs, gives birth to live nymphs, producing about nine generations per year. You’ll often see both adults and nymphs munching in the whorls or upper parts of corn plants. Here, they excrete a sticky, sugary substance known as honeydew in June and July.

Silk

Japanese beetles can block fertilization and stop corn kernels from growing and developing in the first 4 to 5 days after the silk appears. Just 4 or 5 beetles eating the silk this early can cut down on your yield. Fortunately, this is only a problem in drought conditions. Japanese beetles also eat leaves but do little damage. June bugs and corn root beetles feed on corn silk as well.

Kernels

Fall armyworms are the larval stage of the fall armyworm moth, which lays its eggs on leaves planted after early June. Even though the larvae eat all parts of the plant, they prefer whorls, kernels, and husks. Begin checking for these larvae in late June and continue until the silks have dried and fallen off. 

Corn earworms are moth larvae as well, this time of the Helicoverpa zea moth. They’re a major agricultural pest that eat corn leaves, tassels, and whorls, although ears are their preferred food. They begin with the silks and proceed into the ear until they’re ready to drop off and form pupae below the surface of the soil. 

Corn sap beetles can be black or brown and sometimes have orange spots. They range between 1/8 and 1/4 in. (3.1 and 6.3 mm) in length. Their eggs are difficult to see because the female lays them inside the plant. Larvae are 1/4 in. (6.3 mm) long and whitish-yellow or pink in color. They are most attracted to corn at harvest time and often appear after corn earworms have damaged the kernels. 

Sap beetles can give kernels a hollowed-out appearance. The adults lay their eggs in the spring and the larvae emerge in late June to early July. There is one generation per year, with eggs completing their growth and development into adult beetles in 30 to 35 days.

How to Get Rid of Corn Pests

Don’t despair! There are ways to save your corn before it’s too late. Here are some great options for dealing with these pests.

Bacteria

Bacillus thuringiensis is a bacteria that naturally occurs in soil. It produces crystalline proteins that are toxic to the larvae of several insects as well as nematodes. Keep in mind that the Bacillus thuringiensis aizawai strain is toxic to bees and should be avoided. One strain has been specially designed to kill the larvae of Japanese beetles and Asiatic beetles. beetleJUS! kills beetles in their adult, larval, and caterpillar stages. 

Smart Planting

Companion plants are another safe way to get rid of pests. Catnip repels Japanese beetles and aphids. Larkspurs, petunias, chives, and nasturtiums are also good for repelling aphids. Chrysanthemums repel Japanese beetles and can be sold to floral supply houses. Clover adds nitrogen to the worn-out soil as well as repelling wireworms and aphids.

Cosmos send corn earworms on their way and are another decorative flower sold by some florists. Radishes and rue repel cucumber beetles. Tansy repels cutworms. Cilantro and garlic repel grasshoppers and garlic also repels stink bug flies. You can plant mint and catmint to repel corn flea beetles. 

Pesticides

Since the invention of DDT in 1939, pesticides have helped to greatly increase agricultural production. This has also increased the number of people growers can feed. In California, the number one agricultural state in the United States, farmers sprayed 358,662 lbs. (162,686 kg) of pesticides onto fields in 2012 alone.

Unfortunately, many pesticides have been linked with some types of cancer and diabetes, especially organophosphates. Insecticides can be so toxic that some growers warn their children not to set foot in agricultural fields.

Pheromone traps use certain scents to attract insects. These traps can eliminate stink bugs, weevils, moths, and beetles.