Pest of the Week - Armyworms

Cutworms and armyworms are the larvae (caterpillars) of several species of night-flying moths in the family Noctuidae.  The armyworm, Pseudaletia unipuncta, and fall armyworm, Spodoptera frugiperda, are generally considered minor pests, but they have the potential for explosive outbreaks in turfgrass.

Natural History

Armyworm Identification - University of Nebraska

Fall Armyworm
The fall armyworm is native to the tropical regions of the western hemisphere from the United States to Argentina. It normally overwinters successfully in the United States only in southern Florida and southern Texas. The fall armyworm is a strong flier, and disperses long distances annually during the summer months. It is recorded from virtually all states east of the Rocky Mountains. However, as a regular and serious pest, its range tends to be mostly the southeastern states.

Typical adult male fall armyworm, Spodoptera frugiperda (J.E. Smith). Photograph by John L. Capinera, University of Florida.

The moths have a wingspan of 32 to 40 mm. In the male moth, the forewing generally is shaded gray and brown, with triangular white spots at the tip and near the center of the wing. The forewings of females are less distinctly marked, ranging from a uniform grayish brown to a fine mottling of gray and brown. The hind wing is iridescent silver-white with a narrow dark border in both sexes. Adults are nocturnal, and are most active during warm, humid evenings. After a preoviposition period of three to four days, the female normally deposits most of her eggs during the first four to five days of life, but some oviposition occurs for up to three weeks. Duration of adult life is estimated to average about 10 days, with a range of about seven to 21 days


Armyworm
Armyworms get their name from their behavior of moving across fields in an army-like fashion. As larvae consume available food sources, they migrate as an army to new host plants. Though they feed primarily on grasses (oats, wheat, fall rye, corn, barley, and forage grasses), they can be a pest of some vegetables (bean, cabbage, carrot, onion, pea, pepper, radish and sweet potato).

The adult moth is uniformly pale brown to grayish brown in color, with a wingspread of about 1 1/2 inches. There is a characteristic small, white spot near the center of each front wing. The eggs are greenish white and spherical and are laid in masses. Mature larvae are about 1 1/2 inches long with a yellowish or grayish ground color, more or less tinged with pink. The dorsum is greenish brown to black with a narrow, broken, light median stripe. A dark stripe on each side includes the black spiracles in its lower edge. The subspiracular stripe is pale orange, mottled, and edged with white. 

Armyworm, Pseudaletia unipuncta or Mythimna unipuncta. (Marlin E. Rice)

Management Strategies

Naturally occurring predators such as ground beetles and rove beetles may be important in keeping armyworm populations low each year. Research conducted by Michigan State University has found over 12 species of parasitic wasps and several flies that commonly attack armyworm larvae.

There are several types of viruses, a microsporidium, and fungi that infect armyworm larvae. A cool and wet spring favors armyworm development while hindering parasite and predator populations.


Additional Information

Noctuidae - Butterflies and Moths of North America

Armyworm Identification - University of Nebraska

Fall Armyworm - University of Florida

The Arthropod Museum - New Mexico State University

Armyworm - University of Illinois - Urbana

True Armyworms - Scout Info Kentucky IPM Pest Information Pages

 Fall Armyworm - Rutgers University