University of Illinois

No. 10/May 29, 1998

Don't Forget About Armyworms in Wheat

Many entomologists throughout the Corn Belt have reported finding an appreciable number of armyworm moths in light traps this spring. The moths started showing up in traps about the same time that we began to capture black cutworm adults. Not surprisingly, some folks now are starting to observe considerable larval armyworm activity in wheat fields. Remember, when the adult armyworms arrive in the Midwest, they seek thick stands of grass or grassy crops such as wheat into which they lay eggs. The eggs have hatched, and the larvae are feeding on wheat leaves.

Robert Bellm, Crop Systems Educator at the Edwardsville Extension Center, reported a fair amount of defoliation in some wheat fields in southwestern Illinois. However, he has not yet observed either significant feeding on flag leaves or head clipping. Wayne Bailey, Extension entomologist at the University of Missouri, has observed head clipping in some fields in southeastern Missouri, so we should be on the lookout for this yield-threatening activity in Illinois very soon.

A detailed discussion of armyworms and their threat to both corn and wheat was printed in issue no. 7 (May 8, 1998) of this Bulletin. However, now that some scouts may come across armyworms as they monitor wheat fields, it's important to repeat some of the information. Young armyworm larvae are pale green and have a looping habit when they crawl. Fully grown larvae are approximately 1-1/2 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 also are noticeable. Obviously, larger larvae cause considerably more injury than smaller larvae.

Look first for armyworms in areas of wheat fields where the stand is dense. Part the wheat plants and sift through the litter on the ground. Treatment may be warranted if you find 6 or more nonparasitized armyworms (3/4 to 1-1/4 inches long) per linear foot of row and before extensive head cutting occurs. Remember that armyworms usually don't cause economic losses in wheat until they begin feeding on the flag leaves or they clip off heads.

Insecticides suggested for control of armyworms in wheat are Penncap-M* (2 to 3 pt per acre), Sevin XLR Plus (2 to 3 pt per acre), and Warrior 1EC* (2.56 to 3.84 oz per acre). Products marked with asterisk (*) are restricted for use only by certified applicators. Follow all label directions and precautions.

On a related note, Robert Bellm also has observed some stem cutting in several wheat fields. He found 4- to 5-inch pieces of cut wheat stems stacked in areas of the field, usually near field edges. Although many growers attribute this to insect feeding, Robert properly diagnosed the "problem" as rodent activity. In the fields he visited, Robert found evidence of vole activity, and we are aware that mice do the same thing. We do not believe that the injury is economic in a wheat field, so proper diagnosis is important.

Another reminder: Watch for armyworm larvae in any corn field that was planted no-till into a grass cover crop or has had an abundance of grassy weeds this spring.

Kevin Steffey (, Extension Entomology, (217)333-6652