HPIPM:Armyworm FC

Author: Frank B. Peairs[1]

Identification (and life cycle/seasonal history)

Mature armyworm, Mythimna unipuncta (Haworth), larvae are 25 to 40 millimeters (1.0-1.6 inches) in length, smooth bodied, and dark gray to greenish black. They are characterized by five stripes, three on the back and two on the sides, running the length of the body. While the stripes on the back are variable in color, the stripes on the sides are pale orange with a white outline. The head is marked with a netlike pattern of black markings.

The armyworm is unable to survive our winters, and armyworm moths migrate into the region in early summer. They lay their eggs in rows or clusters on the lower leaves of various grass crops. Dense grassy vegetation is preferred for oviposition. Newly hatched larvae move with a looping (inch-worm) action. Larvae feed at night and on cloudy days, hiding under crop debris during sunny periods. One or more generations may occur per year.

Plant Response and Damage

Armyworm feeding is mostly limited to grasses, although this insect will feed on a number of other plants when starving. In Colorado, armyworm is mostly a pest of corn and spring grains. In corn, larvae may later enter the ear tip.

Management Approaches

Chemical Control

Armyworms migrate in to corn from grasses or onto corn within grassy cornfields. They are mostly a problem later in the season. They feed on the corn plant from the bottom leaves upward. If the infestation threatens to consume the lower third or more of the foliage before hard dent stage, chemical control may be justified. It is unknown if control can be expected with Bt corn hybrids.

Due to constantly changing labels, laws and regulations, the sponsors of this web site assume no liability for the suggested use of any chemicals noted in the management section. Contact your local pest management personnel for current information on labeled pesticides that can be used for the intended plant disease, insect pest or weed.