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Worms attacking soybeans, cotton

Three types of caterpillars are defoliating soybeans, cotton and pastureland across millions of acres in Arkansas, according to Gus Lorenz, Extension entomologist for the University of Arkansas Division of Agriculture.

“We’re seeing activity from three caterpillar-type pests: bollworms, webworms and fall armyworms,” said Lorenz. “The outbreak of garden webworms is the worst I’ve seen.”

Webworms have been chowing down on soybean acreage across the state.

“I’ve received calls as far north as Joplin, Mo., and the Bootheel, all the way down to south Arkansas and into Louisiana and Mississippi. It’s been pretty destructive to a lot of late-planted beans that didn’t need this damage.”

Lorenz estimates that some 400,000 to 500,000 Arkansas acres had to be treated with a lot more acreage that didn’t receive treatment.

“Millions of acres got hit with them, some worse than others.”

In addition to webworms are grass-loving fall armyworms. “It’s a pretty good population for this time of year.”

Rain has added to the woes. Soybean farmers who would normally be treating fields for grass were kept away due to the wet weather. The grass grew and became an inviting environment for the armyworms.

“When they sprayed their grass with herbicide, the worms moved off the grass and into the soybeans. There are a lot of acres defoliated from fall armyworms and now I’m getting calls about armyworms in pastures.”

Bollworms are a growing threat as well. During the last week of June, the numbers of trapped moths jumped as part of a normal surge. However, the numbers have stayed elevated since — which is abnormal.

“We were averaging 400 to 500 moths per trap every time we checked them.”

Moths looking for hosts found only a limited amount of cotton and “a lot of these moths are going to soybeans now. They are also causing damage in cotton and milo and tomatoes and everything else. They’re very versatile pests and feed on a lot of different crops.”

The numbers are so high in cotton that growers have to use pesticides in crops specially bred to resist bollworms, such as Bollgard II and Bollgard.

“When we get numbers like we saw towards the front end of July, it overwhelms the technology and we get survivors that we have to spray in order to reduce possible damage caused by the worms,” said Tom Barber, Arkansas Extension cotton specialist. “This gets frustrating because cotton producers already pay high prices for the technology and they expect it to work flawlessly.”

Frustrating may be putting it mildly.

“I just got off the phone with a farmer who’s really angry about it,” Lorenz said. He added that the insects were affecting his research work. “We’re kind of like farmers — we do a lot of plot work and when it’s like this, it’s about to kill all of us too.”

Lorenz said tests in Arkansas found that the bollworm survival rate under pyrethroid treatment jumped from below 10 percent to 48 percent. He believes these worms are survivors of treated fields in south Texas and Mexico. Texas’ drought has been conducive to bollworm growth.

“All these insects are pretty cyclical,” Lorenz said. “Some years are just worst than others and this is a bad one.”

TAGS: Soybean
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