Each spring seedling corn is attacked by a variety of caterpillars, such as cutworms, stalk borers, hop vine borers, and sod webworms. The cutworms are responsible for most of the early-season leaf feeding and stalk cutting. Although very little, if any corn, has emerged, dingy cutworms are being found in the field. Identification is the first step in integrated pest management in determining if there is a potential problem from insects. This article discusses identification of the three most common cutworm species in Iowa and the injury they cause to seedling corn.

Black cutworms less than 1/2 inch long feed on leaves whereas larger larvae can cut or drill plants. Almost all cutworm damage to corn is caused by this caterpillar. Cutting can occur below the surface when the soil is dry, or above ground when the soil is wet and tight around the plant. Cutting rarely occurs after the fifth true-leaf stage but cutworms can drill into the side of the stalk. The black cutworm does not overwinter in Iowa. Eggs are laid in the spring when moths fly into the state from Texas.

Dingy cutworms eat leaves on young corn plants and the leaf injury is similar to that caused by black cutworms. However, this insect rarely cuts corn, therefore it is important to determine if the leaf feeding is from black or dingy cutworms. This insect hatches in the fall and overwinters in Iowa as a partially-grown larva. Larvae 3/4 inch long have already been found in the field this spring.

Black (left) and dingy (right) cutworms are identified by their skin texture. Blacks have grainy skin like sandpaper, while dingys have smooth skin. Identification also is based on the size of the four tubercles (bumps) along the top center of each body segment. On the dingy cutworm, these tubercles are approximately the same diameter. On the black cutworm, the inside pair of tubercles is about 1/3 to 1/2 the size of the outside pair.

Sandhill cutworms injure leaves and cut plants, just like the black cutworm. However, this cutworm only occurs in areas of very sandy soil. Most of the cutting will occur below the soil surface. Injury first appears as wilted leaves, then as dead plants. This cutworm is light tan, semi-translucent, and has several pale, longitudinal stripes. It hatches in the fall then overwinters as a partially-grown cutworm.