Winter conditions in western Nebraska this year have been conducive to the overwintering of some insects. Of particular concern to crop producers is the cutworm.
Damaging populations of army cutworms have already been reported in alfalfa and wheat in northwest Kansas. As conditions gradually warm up, insect activity will increase and growers should be scouting for insects, particularly cutworms, in wheat and alfalfa.
In western Nebraska, the most damaging cutworm is the army cutworm (Figure 1). Economic damage from other cutworms, such as the pale western cutworm, dark-sided cutworm, and variegated cutworm, is rare. The army cutworm damages alfalfa, wheat, and sugarbeet as well as various rangeland grasses.
In late September and October, army cutworms lay 1,000 to 3,000 eggs directly on bare soil, such as in newly planted winter wheat or heavily grazed patches of range. After rainfall, eggs will hatch over an extended period, leading to a variety of caterpillar sizes feeding and developing as long as temperatures are adequate. When the weather turns colder, the caterpillars burrow down into the soil to spend the winter. Come April, large larvae can sometimes be abundant in winter wheat fields.
In 2011, moderate populations of the adult army cutworm moth (or “miller moth”) could be found in sheltered areas during the day. These moths contributed to a large population of larvae in 2012 and high populations in turn contributed to large populations in spring 2013. As we move into April and wheat breaks dormancy, this would be a good time to scout for cutworm activity.
Scouting and Treatment Recommendations
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 established alfalfa stands, use a threshold of two or more larvae per square foot. New or stressed stands of alfalfa require a lower threshold because they are more prone to damage from cutworms. Army cutworms only feed at night and seek out dark sheltered areas during the day, so turn over clots of loose soil and residue for accurate cutworm counts (Figure 2).
If army cutworm counts are above the threshold, consider an insecticide application. Always read pesticide instructions carefully before use.