Cut corn plants have been detected in South Dakota. The damage is due to black cutworm feeding. Black cutworm is a migratory moth that moves into South Dakota during early spring from the Southern Unites States. Although black cutworm caterpillars injure corn by feeding on leaf tissue, the serious damage occurs when caterpillar feeding results in the cutting of young corn plants, leading to significant stand loss and the possible need to replant sections of a field.
Fields with residue or weeds are more attractive to the moths, which may result in increased risk. No-tilled fields and low-lying areas are typically the most attractive for the black cutworm moths. Although most of the corn in South Dakota is past the point where cutworms can cause cutting, late-planted fields or fields that had delayed emergence can still be at risk and should be scouted.
Black cutworm caterpillars range in color from light-gray to brown to black and have a pale band that runs the length of the body along the top of the caterpillar. Caterpillars appear to have rough or “pebbly” texture because their skin is covered with pairs of uneven-sized spots or tubercles located on the sides and near the top of each abdominal segment. These spots or tubercles can be used to separate black cutworm from dingy cutworm (dingy cutworms have equal sized spots), which less-frequently damages corn. Head capsules of black cutworm caterpillars have two black stripes. Black cutworm caterpillars also have three pairs of true legs and four pairs of abdominal prolegs. When fully mature, caterpillars are approximately 1.5 inches in length.
Adult black cutworms are small, brown moths that are difficult to separate from the myriad of other small brown moths observed in South Dakota. Distinguishing characteristics of black cutworm moths include the last third of the forewing being lighter in color compared to the rest of the wing, forewings patterned with dagger-like black markings and hindwings that are typically white or gray.
Scouting for black cutworm is difficult, because caterpillars are nocturnal and hide during the day. Therefore, scouting revolves around finding corn plants with signs of caterpillar feeding, either on the leaves, around the base of the stalk or the presence of cut plants. Scouting should begin during corn emergence (VE) and continue weekly until V5 leaf stage. An insecticide treatment is recommended if greater than 5% of corn plants are cut and any black cutworm caterpillars that are found are less than one inch in length.
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