Army cutworm, Euxoa auxiliaris
Army cutworm adults are commonly known as miller moths and become a household nuisance following outbreaks. During outbreak years they can cause extensive damage in alfalfa, corn, wheat, and numerous other crops. As adults, they are grey-brown moths, with a distinct circle and kidney bean shaped pattern on their wings. Noctuid moths are commonly active during the night and hide in vegetation at or just below soil level during the day. The larvae are the damaging stage of the army cutworm and are 3.8-5 cm (1.5-2 inches) long with two orange and dark stripes down their sides and one white stripe down their back.
- Army cutworm adults are commonly known as miller moths and become a household nuisance following outbreaks.
- Army cutworms have a wide host range and feed on most crops grown in Colorado.
- Larvae are 3.8-5 cm (1.5-2 inches) long when mature, green to black in color, with two dark and orange alternating stripes down their sides, with a pale white line down the back.
- Adults are 3.8-4.5 cm (1.5-1.75 inches), dark grey-brown, with a distinct kidney bean shaped wing marking.
Army cutworm adult. Image credit: John Capinera, University of Florida, Bugwood.org
Army cutworm larva. Image credit: Frank Peairs, Colorado State University, Bugwood.org
Army cutworm pupa. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Life history and habits
The army cutworm has one generation per year. Eggs hatch in the fall following a rainfall, and early-stage caterpillars live through the winter, feeding on warmer days. As daytime temperatures rise, the army cutworm feeds more frequently at night and is found under soil clods or debris during the day. Pupation occurs below the soil. Moths emerge in May and June and migrate to higher elevations to escape high summertime temperatures. These moths are the “millers” that become a household nuisance following outbreaks. In late summer and early fall, the moths return to the plains to lay their eggs in wheat fields and other cultivated areas.
Army cutworms have a wide host range and feed on most crops grown in Colorado. They feed on just about any crop, although are mostly a pest of winter grains, sugar beet, and alfalfa. Army cutworm larvae is mainly a nocturnal foliage feeder, but when foliage is scarce, they will damage crowns of plants and may cut them, causing lodging.
Fields should be monitored periodically during late winter and early spring while the larvae are small. Once the larvae have reached full size, most of the crop damage has been done and treatment is not recommended. To scout for army cutworm, dig and sift soil in a 12 foot area for larvae in multiple locations per field. In thin or dry small grains crops, two or more larvae per square foot is enough to consider treatment of the crop. In healthy small grains crops, four or more larvae per square foot should indicate the need for treatment.
Because of the sporadic nature of outbreaks, management is limited to insecticides. A more comprehensive treatment guideline by crop can be found at: https://www.ag.ndsu.edu/publications/crops/the-armyworm-and-the-army-cutworm
Additional information can be found here, http://extension.colostate.edu/topic-areas/insects/miller-moths-5-597/.
Utah State University. (n.d.). Army Cutworm/Miller Moth. Utah State University – Extension. Available https://extension.usu.edu/pests/schoolipm/structural-pest-id-guide/army-cutworm
Michaud, J. P., and R. J. Bauernfeind. 2014. Army Cutworm. Kansas State University – Cooperative Extension. Available https://bookstore.ksre.ksu.edu/pubs/mf3150.pdf