Pale western cutworm, Agrotis orthogonia
Order: Lepidoptera
Family: Noctuidae
Description
Adult moths are light gray and have a wingspan of about 3.8 cm (1.5 inches). The forewings have a white undersurface and several distinct cross lines on the tips. Young larvae are about 1.3 cm (1/2 inch) long with smooth, gray-white bodies, while mature larvae are 3.8 cm (1.5 inches) and develop a gray-green color. The caterpillars of pale western cutworm lack any distinct markings and can be confused with armyworm caterpillars. However, armyworm caterpillars are generally larger and have distinct stripes.
Quick Facts
- Pale western cutworm is a major pest of winter grains but can also feed on other crops such as corn, sugar beets, alfalfa, and other small grains. This species is a subterranean cutworm, feeding on stems at the crown. Feeding results in severed stems, and entire fields may be lost in a matter of days.
- Mature larvae are 1.5 inches long, smooth-bodied, and a white or greyish color.
- Larvae prefer loose, sandy, or dusty soil and are found most easily in the driest parts of the field, such as hilltops.
- Outbreaks are associated with dry conditions during the previous spring
Adult of pale western cutworm. Image credit: John Capinera, University of Florida, Bugwood.org
Larva of pale western cutworm. Size comparison between a caterpillar and a penny. Image credit: Phil Sloderbeck, Kansas State University, Bugwood.org
Larva of pale western cutworm. Image credit: Frank Peairs, Colorado State University, Bugwood.org
Armyworm larva, Mythimna unipuncta, which is commonly confused with pale western cutworm. Distinguishing features of armyworm larvae include a larger body size and the presence of stripes. Image credit: Frank Peairs, Colorado State University, Bugwood.org
Life history and habits
Adult moths emerge from the soil in late summer and fall. Peak flights generally coincide with tillage and planting of winter wheat. The moths are most active at night, and peak egg laying typically occurs in September. Eggs are laid in the top 1.3 cm (1/2 inch) of loose soil in clusters of 30 to 40 eggs, and a single female can lay 250-300 eggs that usually hatch in late winter. Eggs can hatch sooner during warm periods of winter when temperatures exceed 21°C (70°F) at the soil surface. In nearby states such as Montana, this can occur in February through March. Larvae prefer loose, sandy, or dusty soil and are found most easily in the driest parts of the field, such as hilltops. They develop through six or eight instars through May and early June. After feeding is complete, larvae move to pupal chambers constructed below the soil surface, which typically occurs in August.
While outbreaks of pale western cutworm are sporadic, this species is a potentially devastating pest of wheat grown in Colorado. Pale western cutworm populations can be expected to increase when the preceding May and June had fewer than 10 days with 1/4 inch of rainfall. However, the pest population will remain very low when the rainfall exceeds 1/4 inch for more than 15 days. This is because rainfall drives larvae to the soil surface where they are more exposed to natural enemies, such as pathogens and predatory birds.
Injury
The pale western cutworm is a subterranean cutworm that primarily feeds at night on stems at the crown. Feeding results in severed stems, and entire fields may be lost in a matter of days. Leaf feeding, wilted leaves and dead tillers are good signs of cutworm feeding. Small grains such as wheat, corn and other crops are attacked by pale western cutworm. They have been known to occasionally host on weeds as well.
Chemical control
Because of the sporadic nature of pale western cutworm outbreaks, management is limited to insecticides. The list of available products may vary depending on their registration status.
CSU Extension Fact Sheet
Download or view the CSU Extension’s PDF fact sheet for your reference.
Additional reading
Hein, G., J. Campbell, S. Danielson, and J. Kalisch. 1993. Management of the Army Cutworm and Pale Western Cutworm. University of Nebraska-Lincoln: Cooperative Extension. Available https://agresearch.montana.edu/wtarc/producerinfo/entomology-insect-ecology/Cutworms/NebGuide.pdf