Montana State University > Kevin Wanner Extension

Cutworms

Cutworms, the larval caterpillar stage of moths in the family Noctuidae, can be serious pests of many crops grown in Montana. During the summer and fall the moths fly at night and they are commonly attracted to lights on homes (the miller moth for example). Many different species are pests of a variety of crops across the US. Army and pale western cutworms (Euxoa auxiliaris and Agrotis orthogonia) are the most damaging species in Montana, although significant infestations of the dingy cutworm (Feltia jaculifera) were reported from the eastern region in 2008. All three species lay their eggs during the summer and fall seasons, in fields and cropland. Army and dingy cutworms hatch and begin feeding in the fall and overwinter as partially developed larvae. Most pale western cutworm eggs hatch in the spring. Army and dingy cutworms feed above ground on the leaves at night, resulting in defoliation. Pale western cutworms feed below ground on the crown and stem, often resulting in dead or wilted plants and stand reduction. Cutworms are nocturnal, look for the caterpillars by lightly scraping the soil surface during the day in areas with damage.

Cutworms can damage a wide variety of crops in Montana, including small grains, pulse crops, potatoes, sugar beets and other field crops. MSU extension entomology along with agents and producers monitor army and pale western cutworms at several sites across Montana using pheromone traps. These traps catch adult moths during August and the first two weeks of September. Year-to-year changes in trap catches can indicate changing populations. Increasing moth populations during the fall can provide a regional warning of increased numbers of the damaging caterpillar stage the following spring. .

In small grains, 4-5 army cutworms and/or 2-3 pale western cutworms per square foot exceed damage thresholds and insecticide treatment is recommended. Pyrethroid insecticides can be used to control cutworms, including: Baythroid XL (1.0 ? 1.8 oz / acre wheat), Mustang MAX (1.28 ? 4.0 oz / acre wheat, triticale) and Warrior 1E (1.92 ? 3.2 oz /acre ? wheat, oats, barley, triticale).