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Armyworms Here and There

June 14, 2002
Thank goodness armyworms did not reach the outbreak proportions we experienced in Illinois last year. Farmers have had enough to worry about this spring. Nevertheless, I have received a handful of reports of armyworm injury in corn, primarily in corn planted no-till into rye, alfalfa, or alfalfa/grass mixtures. The reports have come from fields scattered across southern, central, and northern Illinois.

Jim Morrison, Extension educator in crop systems at the Rockford Extension Center, observed armyworms in a few no-till cornfields in JoDaviess County on June 7. The corn had been planted in early May and sprayed with Roundup either just before or shortly after planting. In one field of 3-leaf-stage corn, the armyworms had "cleaned house," leaving only stubs about 2 inches tall. Armyworm injury in other fields was less extensive. The armyworm larvae ranged in size from very small to about 3/4 to 1 inch long. Randy McElroy, an agronomic research manager with Monsanto Company, observed second-instar armyworms in a minimum-tilled cornfield in Hamilton County on June 12. He found as many as three larvae on one V4-stage plant; an average of 18% of the plants had been fed on. This report is important to note because the armyworm larvae are far smaller this year than they would have been at this same time last year.

Although we're into the time of season when corn rootworms and European corn borers capture most of our attention, other insects are still present and causing injury in some fields. As you scout for any insects in corn, keep an open mind about what you might encounter. Our extended cool, wet spring weather has slowed development of most insects, so people are observing insects that usually aren't of any concern at this time of year.

Look for armyworm larvae in fields most likely to be infested (e.g., no-till cornfields in which grass was plentiful). Also keep an eye on fields of corn adjacent to fields of wheat. Although we have had few reports of armyworms in wheat, it's still possible for more mature worms to crawl from wheat into corn when wheat no longer is acceptable as a food source. If armyworms are still small and causing extensive leaf-feeding injury, control may be justified. Refer to Bulletin issue no. 5 (April 26, 2002) for information about scouting, thresholds, and insecticides suggested for control of armyworms.--Kevin Steffey

Author: Kevin Steffey

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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