True Armyworm: April - June
True armyworm is one of several armyworm species, which all get their name from a behavior exhibited by a few species: large numbers of larvae may migrate from a depleted food source.
True armyworm (Mythimna unipuncta [Haworth]) moths migrate to the Midwest from southern states each spring. Mated females prefer to lay eggs in fields with grassy weeds or cover crops, such as rye. Young larvae will feed on these hosts until they are consumed or terminated, at which time they move to corn. It is difficult to predict when and where true armyworm will occur, so it is essential to monitor their arrival by using pheromone traps.
True armyworm larvae feed on the leaves and cause severe defoliation to corn in any stage. Young corn plants can be completely defoliated. Larvae begin feeding at the edge of the leaf and consume all but the midrib. They also begin feeding on lower leaves and move to upper leaves. Young corn plants can typically overcome severe defoliation.
Management practices include insecticides or Bt corn hybrids. Managing grassy weeds near crop fields can reduce true armyworm problems.