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. It is important to scout for their leaf feeding, to correctly identify the species of cutworm causing the injury, and to determine the potential for stalk cutting. This article tells how to identify the three most common cutworm species in Iowa and describes the damage they cause to seedling corn.

Black cutworms less than 12 inch long feed on leaves, but larger larvae can cut or drill plants. 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. Eggs are laid in the spring when moths fly into Iowa from Texas.

Dingy cutworms eat leaves on young corn plants. The leaf injury is similar to that caused by black cutworms. However, because this insect rarely cuts corn, it is important to determine if the leaf feeding is from black or dingy cutworms. This insect overwinters as a partially-grown larva, and it is not uncommon to find it in the field in April.

Black (left) and dingy (right) cutworms are identified by their skin texture. Blacks have grainy skin like sandpaper, and dingys have smooth skin. Identification also is based on the size of the four dark tubercles (bumps) along the top center of each body segment. Do not compare tubercle size on the side of the body. On the dingy cutworm, these tubercles are approximately the same diameter. On the black cutworm, the inside pair of turbercles is about 13 to 12 the size of the outside pair.

Sandhill cutworms injure leaves and cut plants just as the black cutworm does. However, this cutworm only occurs in areas of very sandy soil. Most of the cutting occurs 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.