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Issue No. 5, Article 4/April 23, 2004

Let's Keep Our Eyes on Armyworms

Articles about captures of black cutworm moths are commonplace in newsletters throughout the Midwest in the spring. Consequently, armyworm moths often are overlooked. We don't have to search our collective memories very far to remember the major armyworm outbreak that occurred in 2001. The outbreak, of course, was preceded by captures of armyworm moths in pheromone traps. We still do not have a lot of information relating the development of armyworm outbreaks to captures of armyworm moths, but the appearance of the moths in traps should at least keep us on our toes.

Ron Hines, senior research specialist at the University of Illinois Dixon Springs Agricultural Center, reported his first capture of an armyworm moth in Massac County during the week preceding March 16. Since then, he has reported captures of armyworm moths in Jefferson County (week preceding April 20), Pope County (weeks preceding March 30 and April 13 and 20), Pulaski County (week preceding March 30), and St. Clair County (weeks preceding March 30 and April 6, 13, and 20). The largest numbers of armyworm moths captured have been in St. Clair County. Check out "The Hines Report" (http://www.ipm.uiuc.edu/pubs/hines_report/index.html) for moth-capture records thus far in 2004.

Armyworm moth.

Are the numbers of armyworm moths captured alarming? Quite honestly, we don't really know. A lot of factors have to fall into place for significant armyworm infestations to develop. However, it's not too soon to encourage people to keep armyworms on the radar screen. Early scouting forays, especially in wheat fields, might give us some clues about the possibility for large infestations to develop in both wheat fields and cornfields a few weeks into the future. In 2001, reports of armyworm infestations in wheat and corn began to accumulate during the first couple of weeks of May. By mid-May, the outbreak was at full roar.

Armyworm moths migrate into Illinois on the same prevailing winds and storm fronts that are used by black cutworm moths. Moths seek rank grass on which to deposit eggs, so wheat fields and corn planted into a grass cover crop or into grassy weeds are prime candidates for armyworm infestations. Corn planted no-till into a rye cover crop is especially prone to severe armyworm problems.

When you get an opportunity, check wheat fields for small armyworm larvae. Armyworms are not easy to find when they are young, but diligent searching might be fruitful. Young larvae are pale green in color, although longitudinal stripes are apparent, and the head is yellow-brown. They move in a looping motion. Older larvae are green-brown and more prominently striped. You can usually see a narrow, broken stripe along the center of the back and three stripes along each side of the body, at least one of which appears pale orange. The tan head is mottled with dark brown. Each proleg (the false, peglike legs on the abdomen of a caterpillar) has a dark band.

Early-season injury to corn plants, caused by armyworm feeding.

Growers will be very busy planting corn and soybeans over the next few weeks, so those of us who work with growers will have to help them out by keeping our eyes open for the development of insect problems. Let us know if you begin to find any signs of armyworm injury in wheat, grass pastures, or corn.--Kevin Steffey and Mike Gray

Kevin Steffey
Mike Gray

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