Eileen Cullen, Extension Entomologist
Spring flights of true armyworm moths into Wisconsin resulted in first generation larvae that feed on corn and wheat. The UW Integrated Pest and Crop Management video below discusses field diagnosis of true armyworm feeding on the two crops, larval ID, and economic thresholds. First generation infestations (late June through mid-July) appear to be scattered and not a widespread problem. The video shows you what to look for and how to scout and manage true armyworm in an IPM program.
Pay special attention to cornfields following a rye cover crop or cornfields where grass weed control measures were delayed. Moths may have laid eggs on the rye or grass weeds and can then move to corn.
The economic threshold for true armyworm in corn is 25% of plants with 2 or more larvae or 75% of plants with 1 larvae. In wheat, the threshold is 3 armyworms per square foot. Treatment thresholds generally apply to larval size of ¾ inch or smaller. When larvae reach 1 inch in length they are nearing pupation and feeding is nearly done.