Economic-Threshold Dynamics of Black and Claybacked Cutworms (Lepidoptera: Noctuidae) in Field Corn 1

Abstract

The ability of the modified Missouri cutworm trap to predict cutworm damage in field corn was investigated in Missouri, Illinois, and Iowa from 1979 to 1981. Black cutworms, Agrotis ipsilon (Hufnagel), and claybacked cutworms, Agrotis gladiaria (Morrison), were associated with stand cutting, whereas dingy cutworms, Feltia ducens Walker, had no discernible effect on the plant stand. Most plant damage occurred in the coleoptile (precollar) and the one-collar stage, with population maturity having a significant effect on the relative number of plants cut per leaf stage. The proportion of surface-cut plants (relative to subsurface-cut plants) declined as plants and cutworm populations matured. Survival of surface-cut plants was much greater than that of subsurface-cut plants. A regression model was developed that predicts yield loss by using as inputs the mean number of black and claybacked cutworms in the 2nd-, 3rd- and 4th-, and 5th- and 6th-instar groups, the expected plant population, and the anticipated yield if no cutworms were present.