Unspoken Truths About Pests: Armyworms

This pest can cost you 15% to 50% in yield loss.
This pest can cost you 15% to 50% in yield loss.
(University of Arkansas)

This pest can cost you 15% to 50% in yield loss

Fields wiped out in a matter of hours. Pests marching from grasses and weeds as host plants and into farm fields and pastures. In the 40 years Gus Lorenz has focused on pests, 2021 marks a first.

“This fall armyworm outbreak is the worst I’ve seen in my career,” says Lorenz, University of Arkansas Extension entomologist. “It’s not just rice, it’s really bad in soybeans. We see a few in cotton, and they’re in grain sorghum and even eating corn.”

armyworm damage
The armyworm moth can feed — and thrive — on more than 300 different types of plants. Photo: University of Arkansas

A PERFECT STORM

This year has been the “perfect storm” in the worst way for the pest, Lorenz says. Torrential rains in May and June caused flooded fields, forcing farmers to replant late. Weedy fields also are the perfect home for destructive armyworms.

“They don’t call them fall armyworm for nothing,” Lorenz says. “They usually strike late, but this year they started early. Everybody‘s got fall armyworms.”

While the late-season pest showed up early in Arkansas, they quietly migrated in masses to the Midwest. Ohio farmers, for instance, have seen historical widespread damage. Curtis Young, entomologist and agricultural Extension educator for Van Wert County, Ohio, says the issue blanketed the state at the end of August and beginning of September. 

“They had a huge emergence of adults when a weather front came through that sucked them up into the jet stream and deposited them in the northern states,” Young says, “so, Indiana, Illinois, Ohio, etc., all got a good dose of them from a weather front.”

While the alfalfa seems to be the biggest victim to armyworms in Ohio, they are also decimating cover crops, turf grass, sorghum and all forages. 

“The moth actually has upward of 300 different types of plants it will feed and thrive on,” Young says. “We weren‘t aware we were supposed to be scouting for them this year, and what really set it off was suddenly the caterpillars got large enough they were stripping the foliage off of all kinds of plants in 24 to 48 hours.”

Before farmers and agronomists even knew to scout, the armyworms had already latched on to fields across the state, with some farmers reporting widespread field damage in just a matter of hours, with alfalfa fields and turf turning brown overnight. 

“There’s about a 10"-to-15" swath in the back of a field that was starting to get eaten up pretty bad, and then within eight to 10 hours, the armyworms had completely gone over this whole field,” says Nick Elchinger, a farmer in Deshler, Ohio. “They move very fast when they’re thick.”

Scouting for the insect can be difficult, Young says. While you might not notice feeding in the beginning, armyworms can lurk in fields, hanging on to foliage at an angle that is hard to spot when scouting from above. 

armyworm facts

WILL PROBLEMS LINGER?

What’s the best way to stop armyworms? Mother Nature and a hard freeze. Young says that will kill development of a pest that doesn’t overwinter in northern states. 

“We need to watch late-season crops, such as cover crops, winter wheat and forage crops, until we finally get a hard freeze that will stop the population that is here now,” he says. “They just came out of the blue, and now we’ll be prepared to look for them in the future.” 

 

Read more from this series, which shares insights on how to control pest problems.

 

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