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Corn farmers return to insecticides to battle rootworm

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A corn field in Iowa in 2012 shows rootworm injury. (Courtesy Iowa State University Extension)
A corn field in Iowa in 2012 shows rootworm injury. (Courtesy Iowa State University Extension)
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Correspondent, Iowa Public Radio

After foregoing insecticides for a decade, some corn growers are returning to chemicals to control their No. 1 pest, the corn rootworm. That’s because the insect has developed resistance to the genetically modified variety known as Bt corn, which kills rootworm larvae when they attack the plant’s roots.    

Darwin Bettin, in Sac County, Iowa, has used Bt corn since Monsanto introduced it – and never had to apply insecticide. But one morning after a storm, he found a big surprise.

“I could see corn laying down in my field and none of my neighbors fields,” Bettin said. “I told my wife if I didn't know better that looks like rootworm damage.”

Turns out larvae not killed by the Bt toxin were back feasting on the corn roots and knocking down the plants row by row. Bettin’s yield was cut in half. 

Now, he’s planting a different variety of Bt corn and adding insecticide to be safe.     

He’s not alone. A survey of Illinois farmers showed as many as half are supplementing Bt corn with insecticide, and one-fourth are returning to chemicals as a precaution, whether they’ve seen the bugs or not.

“I would expect that’s probably accurate for Iowa as well,” said Erin Hodgson, an entomologist at Iowa State University. “We kind of loved (Bt corn) to death.”

Farmers found the seed so effective, they abandoned other pest control protocols, including rotating crops to break the insect’s cycle, she said. And rootworm resistance is inevitable for Bt traits currently on the market, Hodgson said, because the toxins are only about 95 percent fatal.  

While the trend is a setback for farmers, it’s a boon for farm chemical makers.

Sales in Philadelphia-based FMC’s agriculture solutions business were up 20 percent in the fourth quarter of 2013 and 9 percent in the first quarter of this year, said Aaron Locker, the company’s marketing director. He said that’s due in part to farmers using insecticides to battle resistance in corn rootworms.

Another concern being raised is that the insecticides now in wider use are potentially dangerous for farm workers who handle them and for the water in nearby lakes and streams.

Back in Sac County, when Bettin lost half his crop to rootworm damage the local seed dealer gave him some money back. But Monsanto didn’t.   

“As much money as those companies  have made off of us selling us those traits over the  years, I  think they'd be willing to step up to the plate when their  trait doesn't work,” Bettin said. 

Luke Samuel, corn insect traits manager for Monsanto said the seed company works with growers so they will be successful.  

“Resistance is not a new concept in agriculture,” he said.    

And, Samuel said, Monsanto is investing millions of dollars in research to bring new products to market.

 While the Environmental Protection Agency says it could restrict the future use of Bt seed, the regulator also says Monsanto is moving in the right direction by introducing new varieties, and encouraging farmers to rotate crops.  

Meanwhile, Bettin is hoping for a good yield this year.

“Right now it looks like a million bucks,” he said. “All’s it’s got to do now is grow.”

And with insecticide at work in the soil, rootworm larvae shouldn’t’ stand a chance. Still, neighbors may see an unfamiliar sight this summer: crop dusters. Bettin said he’ll apply more insecticides from the air to ensure the rootworm doesn’t survive to infest the ground with larvae next year.