March 14, 2012

Nebraska’s mild winter is expected to lead into warm, dry conditions in the early spring. These conditions are conducive to the survival of some insects that overwinter in this region. One group of particular importance are cutworms.

Figure 1. With the recent warm-up army cutworms are likely to start feeding in western Nebraska wheat fields. Field scouting now can help determine whether treatment is necessary.

In western Nebraska the most damaging cutworms are primarily the army cutworm (Figure 1) and rarely, the pale-western, dark-sided, or variegated cutworm. The army cutworm is the most destructive cutworm to crops including alfalfa, wheat, and sugarbeet as well as various grasses found on rangeland. In late September and October, army cutworms lay 1,000–3,000 eggs directly on bare soil, such as newly planted winter wheat or heavily grazed patches of range. After rainfall, eggs will hatch over an extended period in the fall, resulting in a variety of caterpillar sizes and stages. They will feed and develop as long as temperatures are adequate. Come April, large larvae can sometimes be abundant in winter wheat fields.

In 2011 moderate populations of the adult army cutworm moth (“miller moth”) could be found in sheltered areas during the day. (See Bradshaw blog post.) These moths may have contributed to a larger population of larvae for 2012. As we continue into March and April and wheat breaks dormancy, this would be a good time to scout for cutworm activity.

Scouting for Army Cutworms

To scout for army cutworms use a treatment threshold of four or more cutworm larvae per square foot of winter wheat or alfalfa. However, for stressed, thin stands of wheat or for newly establish alfalfa stands, use a threshold of two or more larvae per square foot. Thin, stressed stands or new stands of alfalfa require a lower threshold because they are more prone to cutworm damage. Army cutworms only feed at night and seek dark sheltered areas during the day, so turn over clots of loose soil and residue for accurate cutworm counts.

Treating Army Cutworms

If army cutworm counts are above the threshold, you may want to consider an insecticide application. See Table 1 for a selection of chemical control products. Always read pesticide instructions carefully before use.

Jeff Bradshaw, Extension Specialist
Susan Harvey, Agricultural Research Technician III
Both at the Panhandle REC, Scottsbluff