HPIPM:Field Key to Insects and Mites Attacking Field Corn

Author: Frank B. Peairs[1]

Insects Affecting Seeds and Seedlings

• Feeding mostly below ground, occasionally some foliage feeding. Dull brown caterpillar with broad pale stripe on back. Somewhat smaller than other cutworms when full grown. Dingy cutworm

• Feeding mostly below ground. Caterpillar with grayish white body without markings. Head has two distinct vertical dark brown bars. Pale western cutworm

• Failure to sprout, or weakened and discolored seedling. Kernel or surrounding soil contains small (¼ inch) yellow or white, tapered larvae, without apparent legs or head. Seedcorn maggot

• Feeding on foliage. Gray to light brown caterpillar with a two rows of yellow dots along back. Variegated cutworm

• Roots chewed off. Roots or below ground portion of stem may be tunneled. Yellow to red larvae up to 1½ inches, with distinct head and legs and ornate terminal abdominal segment. Wireworms

Insects Affecting Roots

• Roots chewed off, sometimes to the main stem. Roots may also be discolored or tunneled. Small (up to ½ inch) yellow or white larvae with distinct brown head. Lodged and/or goosenecked plants may be present. Continuous corn only. Western corn rootworm

Insects Affecting Leaves

• Leaves with yellow spots along midrib. Dead areas of leaves or entire leaves in more severe cases. Damage progresses from lower leaves. More common in field edges and drier parts of field. Undersides of damaged leaves covered with webbing, microscopic green mites, and clear round eggs. Banks grass mite

• Ragged leaf feeding in whorl. Large green or brown caterpillars with skin covered with microscopic spines (visible with 10X hand lens). Corn earworm

• Leaves covered with masses of blue green, soft bodied insects. Yellowish or reddish discoloration may be present. Corn leaf aphid

• Narrow, elongate feeding lesions on upper leaf surfaces, along with sawdust-like material. Perpendicular rows of round holes ("shot-holing") may also be present. Flesh-colored caterpillars with faint spotting. European corn borer

• Ragged feeding on leaves late in season. Dark, irregularly striped caterpillars. Fall armyworm

• Ragged feeding on leaves, usually in field margins. Entire leaves often eaten to midrib. Grasshoppers

• Ragged feeding on leaves late in season. Similar to fall armyworm but feeding more likely to progress from bottom of plant and edges of feeding holes ragged rather than smooth. More common in areas of field with grassy weed problems. Dark, irregularly striped caterpillars with light-colored mottling on head. Armyworm

• Similar to Banks grass mite, but damage not progressive from lower leaves and leaf tissue on opposite side of leaf from colonies less likely to be discolored. Damage rare before flowering. Positive identification of both mite species should be left to an expert. Twospotted spider mite

• Elongate skeletonizing of upper leaf surfaces, usually just before pollen shed. Small, active brown or black beetles, often with yellow stripes on back. Western corn rootworm

Insects Boring in Stalk

• Stalk tunneled. Tunnels may contain flesh colored caterpillars with faint spotting. European corn borer

• Stalks tunneled by cream-colored caterpillars with distinct brown or black spots. Plants may break just above ground because of internal feeding. Larvae lose spots in fall and winter. Limited to southeastern Colorado. Southwestern corn borer

Insects Found on Tassel

• Tassels covered with masses of blue-green, soft bodied insects. Yellowish or reddish discoloration may be present. Corn leaf aphid

• Tassel tunneled, may break due to damage. Flesh-colored caterpillars with faint spotting. European corn borer

• Small, active brown or black beetles, often with yellow stripes on back feeding on tassel during pollen shed. Western corn rootworm

Insects Affecting the Ear

• Damage to silks and ear tip. Single large green or brown caterpillar with skin covered with microscopic spines (visible with 10X hand lens). Corn earworm

• Shank, ear, ear tip tunneled. Parallel rows of kernels damaged. Tunnels may contain flesh-colored caterpillars with faint spotting. European corn borer

• Silks, ear tips and ears damaged. Entrance to ear may be through husks rather than just through silks. Dark, irregularly striped caterpillar. Fall armyworm

• Silks, husks and ear tip damaged. Usually accompanied by signification defoliation. Grasshoppers

• Silks chewed down to ear tip, with little damage to husks. Small, active brown or black beetles, often with yellow stripes on back. Western corn rootworm

• Silks, ear tips and ears damaged. Entrance to ear may be through husks rather than just through silks. Light brown caterpillar with lighter stripes. Three dark brown vertical bars on "collar" just behind head. Western bean cutworm

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.