Army cutworms.
Army cutworms.

Army cutworms have been spotted feeding on winter wheat seedlings in fields located in South Dakota. The specifics for South Dakota are pertinent to many other winter wheat fields outside of the state. An Extension specialist also provides identification specifics.

"The early spring and warm temperatures helped the greening of winter wheat fields all over South Dakota also favoring the insect's development," said,Anitha Chirumamilla, SDSU Extension entomology field specialist.

Chirumamilla explained that fields planted early last fall could have higher chances of army cutworm infestation as lots of growth before dormancy attracts adult moths that lay their eggs in the soil.

"Army cutworm, Euxoa auxiliaris, is a very common species of cutworms attacking wheat in South Dakota," she said.

The larvae are greyish in color with pale markings and a light stripe on their backs. Adult moths lay eggs in the soil during fall season and overwinter as larvae.

With the onset of spring, the larvae resume their development by feeding on the seedlings. Full grown larvae can be two-inches long. "Damage is caused by larvae feeding on the leaves. Most of the damage occurs during evening hours as the larvae are sensitive to light and hide in the soil near the plants during the day," Chirumamilla said.

Larvae can be seen during daytime on cloudy days.

Scout wheat & alfalfa fields for army cutworm

Larvae can move in masses resembling an army to nearby vegetation in search of food. "First-year alfalfa is also highly vulnerable to damage by army cutworms," she said.

Chirumamilla encouraged growers to scout their fields for army cutworm larvae by digging the soil around the plants.

In healthy plant stands, an insecticide treatment is recommended at four or more larvae per square foot, but when the stand is thin, and plants are stressed, the threshold is much lower at two or more larvae per square foot.

"Areas where cutworms have been spotted were well over the action threshold and spraying is critical to avoid serious damage," Chirumamilla said.

Several organophosphate and pyrethroid insectides are registered for cutworms control in wheat. Information about insecticides labelled for army cutworm management and recommended dosages are available in the 2015 South Dakota Wheat Pest Management Guide found at iGrow.org/up/resources/03-3033-2014.pdf.