Corn, or maize, is a foundational global crop, providing food, feed, and fuel. Its high caloric and nutritional density make it a favored target for a wide array of organisms throughout its life cycle. Successful cultivation requires understanding these biological threats, which range from microscopic insects to large mammals. Effective management depends on accurately identifying the specific pest based on the distinctive damage it leaves behind.
Insects That Attack Corn Roots and Stalks
Some of the most destructive pests target the corn plant at its most vulnerable stages, often below the soil surface where damage goes unseen until severe. Corn rootworm larvae, a significant threat, feed directly on the roots, impairing the plant’s ability to absorb water and nutrients. This feeding can lead to stunted growth and a characteristic condition known as “goosenecking,” where the plant lodges or falls over, then attempts to grow upright again at the node.
Wireworms, the larvae of click beetles, cause damage early in the season by tunneling into the germinating seed, sometimes hollowing it out completely. Their feeding results in stand reduction, appearing as distinct gaps in the rows where seeds failed to emerge. Wireworms may also bore into the underground stem of young plants, causing them to wilt or become stunted.
Cutworms are caterpillar larvae that often cause damage just at or below the soil line, resulting in the complete severing of young corn seedlings. This damage is most common in small plants, typically those with six leaves or fewer, leading to significant stand loss. Growers can confirm the presence of cutworms by gently excavating the soil near a recently cut plant, as the larvae often hide close to the severed stem during the day.
Pests Targeting Corn Leaves and Ears
As the corn plant matures, insect threats move to the visible parts of the plant, compromising photosynthesis and directly reducing grain yield. The European corn borer is an internal feeder. First-generation larvae initially cause “shot-hole” damage on the unfurling leaves as they chew through the whorl tissue. Later generations bore into the stalk, leaving sawdust-like excrement, called frass, near the entry hole, which weakens the stalk and can lead to breakage or dropped ears.
Armyworms are leaf-feeding caterpillars that prefer the tender foliage in the whorl, often resulting in ragged edges on the leaves. True armyworms frequently migrate in large numbers from grassy areas into corn fields, consuming leaf tissue and leaving behind brown frass in the whorl or leaf axils. In severe infestations, they may consume all the leaf tissue, leaving only the tough midribs.
The corn earworm is a primary pest of the developing ear. The larvae enter through the silk channel to feed on the kernels at the tip. This feeding results in chewed kernels and is easily identified by the moist, brownish frass packed between the silk and the ear tip. The damage causes direct kernel loss and creates entry points for fungal pathogens that can lead to ear rot.
Small sap-sucking pests, like aphids and spider mites, feed on plant fluids, causing discoloration and stippling on the leaves. Spider mites are often found on the underside of leaves, producing fine webbing and causing a yellow or whitish spotting that can resemble drought stress. Corn leaf aphids secrete a sticky substance called honeydew, which can attract sooty mold, further interfering with the plant’s photosynthetic ability.
Non-Insect Threats to Corn Crops
Larger vertebrates present a different set of challenges, often causing localized, but intense, damage near harvest time. Raccoons are notorious for attacking ears during the milk stage, pulling down stalks haphazardly to access the sweet kernels. They typically peel back the husk and chew off parts of the cob, leaving behind shredded husks and partially eaten ears.
White-tailed deer cause damage throughout the season, from browsing young leaves and stalks to consuming the developing ear. Deer often scrape kernels from the ear using their lower incisors, leaving a distinct pattern unlike the tearing or chewing of raccoons. Their foraging sometimes results in “decapitated” plants or ears, and their presence is often confined to outer rows or areas adjacent to wooded cover.
Birds, such as blackbirds and crows, target corn at two main stages: the seed and the soft kernel. They will attack seedlings by digging around the entire plant to pull out the seed before it is exhausted, causing stand loss. Later, they peck at the soft kernels on the ripening ear, leaving characteristic cup-like holes and shredded husks.
Integrated Protection and Management Strategies
Managing corn pests effectively involves adopting an Integrated Pest Management (IPM) approach that combines multiple control tactics based on pest identification and life cycle knowledge. Cultural controls are foundational. Crop rotation is particularly effective against immobile pests like the corn rootworm, whose larvae cannot survive when a non-host crop like soybean is planted in the following season. Adjusting the planting date can also help the crop avoid periods of peak pest activity.
Mechanical and physical controls offer direct intervention without relying on chemical application. Tilling the soil can destroy crop residue where pests like the European corn borer overwinter as larvae, breaking their life cycle. For visible pests like armyworms or cutworms, handpicking or applying a layer of sand or fine soil to the whorl can physically disrupt their feeding. Physical barriers, such as specialized electric fencing or netting, are employed to exclude larger threats like deer and raccoons.
Biological and genetic controls are important components of IPM programs. Planting corn hybrids that express toxins from the bacterium Bacillus thuringiensis (Bt) provides built-in protection against several lepidopteran pests, including corn borers and corn earworms. Encouraging beneficial insects like lady beetles, lacewings, and parasitic wasps, which naturally prey on aphids and corn earworm eggs, helps keep pest populations below economically damaging levels.