Armyworms Being All they Can Be in Southern indiana

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An unfriendly army is marching through southern Indiana, and new battalions may soon mount offensives in other parts of the state.

Armyworms, so named because they appear to move in unison across fields, are chewing up emerging corn plants, wheat, rye and other tall growing grasses.

Extensive feeding damage has been reported in counties south of Interstate 74, with the most severe damage concentrated south of Greene County and west of Perry County.

Jerry Nelson, Purdue University Extension educator in Knox County, said his county has been hit especially hard.

"The damage I have seen ranges from complete devastation in pastures to wiping out cornfields to actually eating soybeans, which is rather unusual," Nelson said. "Thousands of acres have been sprayed in Knox County."

Replanting may be in order for farmers with severe armyworm damage, Nelson said.

Why the armyworm population is so high this spring is a mystery, said John Obermeyer, Purdue entomologist. Hot, dry weather may be a contributing factor, he said.

Obermeyer visited Knox County Tuesday and witnessed the damage firsthand. One farmer told Obermeyer armyworm larvae destroyed his pasture, then began feasting on his adjoining lawn.

"I also observed them eating soybeans. If left with no choice, they'll eat just about anything," he said.

Armyworm larvae range in size from one-fourth inch to 1.25 inches long. Damage usually appears insignificant when the larva hatches. "Then, what seems like overnight, the armyworm are a half-inch to 1 inch long and devouring crops," Obermeyer said.

When armyworms consume all available green leaf material in a field, they'll move into adjacent fields. The feeding frenzy ends when the larva buries itself in the soil to pupate. In late summer the adult moth emerges and begins laying eggs.

"Treatment decisions for armyworm cannot be put off long because of their ability to decimate a crop in days," Obermeyer said. "Several pesticides are available for treatment, but one needs to be aware of harvest restrictions on the product label. For example, with pastures you can spray with malathion while the cattle continue grazing, while with Sevin-brand pesticide you must remove the animals for two weeks."

Armyworm infestation could spread to northern Indiana counties in the days ahead. Larvae likely are hatching now, Obermeyer said.

"Northeastern Indiana concerns me the most, because it has a lot of those tall growing grasses associated with their crops and pastures because of the dairy industry," he said.

Three weeks ago Purdue entomologists caught 670 armyworm moths in black light traps in Whitley County.

"I don't know that we've ever had a count that high," Obermeyer said. "Typically, we would find numbers only in the teens or twenties at the most. You've heard the expression 'a heart attack waiting to happen'? This is an armyworm infestation waiting to happen."

Armyworm damage has been reported in Texas, Kentucky and Illinois. The pests were so thick in one part of Illinois that a churchgoer had to sweep worms off the door and steps before services Sunday. Several Illinois motorists said roads appeared to be moving as armyworms crossed from one field to another. Additional information on armyworms and pesticide options is available in the story, "Armyworms Marching Big Time, This is NO Parade," by Obermeyer and Purdue entomologists Rich Edwards and Larry Bledsoe. The story appears in the May 18 issue of Purdue's Pest & Crop Newsletter. The newsletter may be downloaded online at http://www.entm.purdue.edu/Entomology/ext/targets/p&c/index2001.htm.