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Issue No. 3, Article 4/April 14, 2006

True Armyworm Moth Captures Reach Impressive Levels in Kentucky

Doug Johnson, extension entomologist, University of Kentucky Research and Education Center, reported that true armyworm moth captures were very large for the first week of April. Captures in two pheromone traps were 290 and 252 moths per trap for the week that ended April 6. Doug also indicated that these totals are greater than observed during the past 4 years and similar to captures that took place in 2001, an armyworm outbreak year. That year, pheromone traps at the Kentucky Research and Education Center were averaging about 400 moths per trap per week by mid-April. These captures do not confirm that an outbreak of true armyworms will occur once again; however, it does make sense to become more familiar with scouting procedures and economic thresholds for armyworm larvae in pastures, small grains, and seedling corn. Doug anticipates finding armyworm caterpillars as early as April 18; however, he believes armyworm larvae will become much more "detectable" by April 27. For producers in southern Illinois, these dates suggest that scouting is just around the corner.


Armyworm moth.


Severe defoliation caused by armyworms in 2001.

Ron Hines, Dixon Springs Agricultural Center, reported that the first true armyworm moths were captured on March 16 in Pope County and on March 17 in Fayette County. On April 4, 16 true armyworm moths were captured, so the flight intensity of this insect pest does appear to be increasing. So far, the captures in Illinois are still well below those reported by Doug Johnson. By going to The Hines Report, you can keep informed weekly of the true armyworm flight this spring across southern Illinois. Trap captures for other insects, such as black cutworms, also are reported by Ron. By going to another useful Web site you can keep track of accumulating pest degree-days and optimize your scouting efforts for true armyworms and other insect pests.

Many readers may recall how widespread armyworm infestations were in 2001. Pastures in many areas of the Midwest suffered significant damage that year. 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.

True armyworm larvae often go unnoticed until the injury is obvious. However, the small, young larvae can be found if you look for them carefully. Young larvae are pale green, although longitudinal stripes are apparent, and the head is yellowish brown. They move in a looping motion. Older larvae are greenish 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 (one of the false, peglike legs on the abdomen of a caterpillar) has a dark band.

Insecticide products for armyworm control in pastures are limited. The 2006 Illinois Agricultural Pest Management Handbook lists Sevin XLR Plus (1 quart product per acre) as an option. If an outbreak of true armyworms does occur, we will provide more information regarding scouting procedures and control options for corn and wheat. Please let us know if armyworms begin to cause significant problems in your area.--Mike Gray

Author:
Mike Gray

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