By Scout Nelson
Army cutworms are becoming more active in South Dakota wheat fields as temperatures continue warming this spring. Farmers are noticing feeding damage in some areas, and experts warn that activity may increase during the coming weeks if warm weather continues. The caterpillars mainly feed at night and hide beneath soil or crop residue during the day, making them difficult to detect early.
Adam Varenhorst, Associate Professor and SDSU Extension Field Crop Entomologist, along with Philip Rozeboom and Patrick Wagner, highlighted that army cutworms are one of the first insect pests commonly observed in wheat during spring because the caterpillars overwinter in winter wheat and alfalfa fields after moths return from the Rocky Mountains during fall.
Army cutworm caterpillars begin feeding when temperatures reach around 40 °F. Young caterpillars are usually light green or light brown with limited markings. Older caterpillars become gray or gray-brown with spots and pale stripes running along the body. Mature caterpillars may cause visible feeding damage by clipping wheat plants near the soil surface, creating ragged patches within fields.
Scouting for army cutworms can require extra time because the insects hide during daylight hours. Farmers often first notice damaged wheat plants before finding the caterpillars themselves. During cloudy days, the insects may remain active above the soil surface for longer periods.
Researchers noted that winter wheat can often recover from moderate infestations because the caterpillars usually feed on leaf blades rather than stems or growing points. However, crop injury may become more severe when fields experience dry conditions or moisture stress.
Management is recommended when large, damaged patches appear or when 2-4 caterpillars are found per square foot. Insecticide applications may help reduce infestations if necessary. Experts recommend applying treatments only when temperatures are expected to stay at or above 50 °F for several days after application because cooler weather reduces caterpillar activity and lowers insecticide effectiveness.
Photo Credit: depositphotos-simazoran
Categories: South Dakota, Crops, Wheat, Alfalfa