Begin Looking for Armyworms as You Scout Wheat Fields

April 23, 1999
Using some tried-and-true sampling techniques, I recently found a couple of armyworm moths: One flew into my open car window, and I flushed the other one out of my grass while mowing my lawn. (Okay, so maybe these are unconventional techniques, but the results were not in question!)

Adult armyworms arrive in Illinois at the same time as black cutworm adults; they probably travel together in the same jet streams. When they arrive, they seek lush grasses in which to deposit their eggs. Consequently, wheat fields and fields with a lot of grassy weeds are ideal oviposition sites. While you are still waiting to scout corn after it gets planted, you might bide your time scouting wheat fields. Although armyworm larvae will not be easy to find at this time of year, careful sifting through the debris on the soil might uncover the small caterpillars. You also might encounter egg masses on wheat leaves.

The armyworm moth is tan to gray-brown with a wingspan of about 1.5 inches. A single, small but prominent white dot in the center of each fore- wing is evident. The female lays small, white eggs in rows or groups on leaves of grain or grass. The moth usually folds the leaf lengthwise and fastens the leaf about the eggs with a sticky secretion. The young larvae, the ones you might find right now, are pale green in color and have a looping habit when they crawl. When the larvae are full grown, they are approximately 1.5 inches long and have distinct longitudinal white, brown, and orange stripes, most notably the orange stripes just beneath the spiracles (breathing pores) on each side of the body. Black stripes on the prolegs (the nonjointed "false legs" on the abdomen) also are noticeable.

Scout for armyworms in wheat in areas of the field where the stand is particularly dense. Look for the larvae by parting the wheat plants and sifting through the litter on the ground. If you find armyworm larvae, make a note, but don't overreact. Small armyworms feed first on the lower leaves. The caterpillars then work their way upward as they grow and consume more leaf material. Armyworms usually don't cause economic losses in wheat until they begin feeding on the flag leaves. Control of small armyworm larvae is not warranted because natural enemies and diseases may cause considerable mortality in the population.

If reports of armyworms or other insects in wheat begin to come into our offices, we will provide thresholds and guidelines for their control.--Kevin Steffey

Author: Kevin Steffey