Armyworm compared to a leaf

Armyworms can come in many different colors


True armyworm larvae are being found across New York State. This native species does not overwinter in NY but fly north from southern states in the spring. Armyworm moth migrations are somewhat sporadic, cyclic from year to year and difficult to predict. True armyworms are primarily a pest of plants in the grass family: forage / pasture /grasses (& lawns), small grains and corn.

Note: Under hunger stress true armyworms will also attack some legumes and other plants. Moths lay their eggs on weeds and/or grasses along field margins, on leaves of corn, or on small grains. Larvae hatch about a week later and develop over approximately a 3 week period, feeding mostly at night.

Commercial field crop situations at risk for armyworms are:

  1. Grass or mostly grass hay fields, pastures
  2. Corn fields that were late planted into grass fields, no-till or reduced tillage fields, fields with crop residue, planted into a small grain (especially rye grass) cover crop
  3. Corn fields with grassy weeds, quackgrass, crabgrass and bluegrass and other perennials
  4.  Small grain fields

True armyworm larvae appear smooth, cylindrical, pale green to brownish when they are still small. Mature larvae are smooth and marked with two orange, white-bordered strips on each side. Larvae range in size from 1/8 inch to 1 1/2 inches long (Information compiled by Schuyler County Cornell Cooperative Extension).

Additional Resources

Armyworm Resources, Cornell University NYS Integrated Pest Management Program

Purdue University Field Crops IPM page discusses several species of Armyworm prevalent in Indiana, how to distinguish the Fall armyworm larvae from several other species, and includes sampling methods and I{M guidelines.

This University of Illinois Extension page on True Armyworm (Mythimna unipuncta Haworth) covers identification, life cycle, discovery, and management practices


Last updated October 26, 2023