Many species of pests, insects, and bugs attack corn and corn plants. 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 send up only weak seedlings the seed corn maggot is the likely culprit. Eggs laid in soil hatch in early spring, thriving at temperatures as low as 40 degrees Fahrenheit. The larvae grow to a quarter inch in length, with pointed heads, tough, yellowish-white skin, and no legs. After eating the larvae form pupae, reddish brown in color. In two weeks the adult form, small flies, emerge, ready to lay more eggs.
Seedlings: Identify the killer of corn seedlings by 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 eat notches into seedlings’ leaves in May. They are brown or gray, about 3/16 of an inch long, often presenting a dusty appearance when covered with dirt.
Roots: Rot sets in from fungus if the soil is below 55 degrees Fahrenheit 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 such nests under during the winter. Adult spotted cucumber beetles lay eggs near corn roots in the autumn. In the spring the yellowish grubs, or southern corn rootworms, hatch and eat the roots, causing plants to blow over in the breeze. Rotating crops and plowing under corn stalks after the harvest help to prevent this insect from making a pest of itself. Roots are also a favorite of corn flea beetles in their larval stages. Asiatic beetles feed on root hairs, weakening the plant.
Stalks and Leaves: Many pests see corn plants like a big, luscious salad. Adult corn flea beetles eat stalks of corn plants growing slowly due to poor nutrition. They are brown and pinhead-sized. 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 9 generations per year. Both adults and nymphs are often seen munching in the whorls or upper parts of corn plants, where they excrete a sticky, sugary substance known as honeydew in June and July.
Silk: Japanese beetles can block fertilization and prevent corn kernels from growing and developing during the first 4 to 5 days after the silk appears. Four or 5 beetles eating silk this early can cut down on yield. Fortunately, this is only a problem under drought conditions. Japanese beetles also eat leaves, but this does little damage. Junebugs and corn root beetles are also known to feed on corn silk.
Kernels: Fall armyworms are the larval stage of a species of moth, which lays its eggs on leaves planted after early June. Although the larvae eat all parts of the plant they prefer whorls, kernels, and husks. Begin checking in late June and continue observing until silks have dried and fallen off. Corn earworms, too, are moth larvae. They are a major agricultural pest, eating corn leaves, tassels, and whorls, although ears are their preferred food. They begin on silks and proceed into the ear until they are ready to drop off and form pupae in the earth. Corn sap beetles can be black or brown, sometimes with orange spots, and range in length between ⅛ and ¼ inch. Eggs are difficult to see because they are laid inside the plant. Larvae are ¼ inch long, whitish yellow or pink. They are 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. Adults lay 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.
Since DDT was invented in 1939 pesticides have greatly increased agricultural production and the numbers of people growers are able to feed. In California, the number one agricultural state in the United States, 358,662 pounds of pesticides were sprayed onto fields in 2012 alone. Unfortunately, many pesticides, especially the organophosphates, have been linked with some types of cancer and diabetes. Insecticides can be so toxic that some growers warn their children not to set foot in agricultural fields. Many insecticides are toxic to bees, which help produce about ⅓ of our food. Fortunately, safe alternatives exist.
Bacillus thuringiensis is a bacteria that naturally occurs in soil. It produces crystalline proteins toxic to larvae of several insects, as well as nematodes. (The Bacillus thuringiensis aizawai strain is toxic to bees, and should be avoided). One strain is specially designed to kill Japanese beetle and Asiatic beetle larvae. BeetleJUS is a strain developed for killing beetles in their adult as well as larval and caterpillar stages. The bacteria should not be handled by pregnant women, as some studies have shown B. thuringiensis to be toxic to human embryos.
Companion plants are a 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 also 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 sends corn earworms on their way and is another decorative flower sold by some florists. Cucumber beetles are repelled by radishes and rue. Tansy repels cutworms. Cilantro and garlic repel grasshoppers, and garlic also repels stink bug flies. Plant mint and catmint to repel corn flea beetles. While pheromone traps use certain scents to attract insects. Stink bugs, weevils, moths, and beetles can be eliminated with the traps.