Below Ground (Soil) Insect Pests

General Information

Most insect pests that attack corn at or below the soil surface are most damaging to seedling corn. Planting corn early can reduce the chances of insect infestations and injury. Controlling soil insects that threaten corn stands and seedling health is important for corn production. Factors such as reduced tillage, no-till corn, and fields with a history of soil insects justify the use of insecticides or insecticide seed treatments at planting. These products are used as prevention, because when there is high potential for infestation rescue treatments offer less control.

Adult Southern Corn Rootworms are also called the twelve-spotted cucumber beetle and have a wide host range. Females lay eggs at the base of corn plants or alternate weed hosts and, after hatching, larvae feed on roots, leading to wilting or lodging (known as “goose necking”) or plant death. The larvae have three pairs of legs just behind the head. Larvae are up to 1/2 inch long with brownish patches on the head and tail end.

• Western or Northern Corn Rootworms are rare pests in Tennessee. However, serious damage is sometimes seen if corn is continuously grown for many consecutive years, as sometimes done in dairy operations. Insecticide seed treatments are much less effective on these species compared with the southern corn rootworm. Because of the biology of these rootworm species, rotating to an alternate crop every 3-4 years is suggested to prevent infestations. Some Bt corn technologies provide excellent control of western or northern corn rootworm, but do not effect southern corn rootworm.

The Seedcorn Maggot is the larval stage of a fly that feeds on decaying organic matter in the soil. Larvae are less than 1/4 inch, pale white, and lack legs or an obvious head. Seedcorn maggots feed on germinating corn seed planted in cool, wet weather or when corn is planted into fields with freshly decaying vegetation.

Wireworms are the larval stage of click beetles. Larvae are usually brown, elongated and slender and may take between 2 and 5 years to mature, depending on the species. Control is often difficult in fields that were fallow or pasture before corn. Wireworms feed on the seed and roots and bore into the underground part of the corn seedling, which can lead to wilting, deadheart, or plant death.

White Grubs are the larvae of scarab beetles (e.g., May and June beetles), and some species feed on the roots of seedling corn plants. Grubs are C-shaped and white to cream in color.

• The Sugarcane Beetle is a scarab beetle that may cause significant economic damage in corn less than two feet tall. Although the larva is a white grub, it is the adults that cause damage by feeding on the stem and roots just below the soil surface. The adult beetle is about ½-inch long, black, with strong legs and coarse spines adapted for digging. The back of the beetle has numerous “pits”. Adults can infest fields after planting. Infestation can be especially severe in fields where Bermudagrass is common.

Cutworms are the larvae of several species of moths which spend much of their time below ground, typically venturing out at night to feed above ground on the stems and leaves of plants. Additional information about the management of cutworms is provided on the cutworm page.