The true armyworm is a migratory pest from the southern U.S. that feeds on the leaf tissue of early and late vegetative corn. Adult true armyworm moths are attracted to fields that contain living ground cover, which include fields with grassy weeds or cover crops such as rye or grass. Fields that are minimum, no-till, or contain a cover crop should be scouted for true armyworms in May and June (Fig. 1). Upon arrival, the female moth will lay eggs onto the living ground cover. After hatching, the young larvae will feed on these plants until the plants are completely consumed or removed with herbicides. When the initial host plants are no longer available, the larvae will then move to corn. True armyworm larvae are identified by dull orange stripes found on each side of their body (Fig. 2). In addition to the six legs found on the thorax of the true armyworm, they also have four prolegs with dark bands on their abdomen (Fig. 3A). True armyworms are also identified by the network of black lines present on their orange head capsule (Fig. 3B). On injured plants, larvae can generally be found in the whorl of the plant.
Iowa State University
Varenhorst, Adam Jerry; Dunbar, Michael Wilson; and Hodgson, Erin W., "True Armyworms Defoliating Corn Seedlings" (2015). Integrated Crop Management News. 318.
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