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Entomologist: Bt Effectiveness to Corn Rootworm is Breaking Down

Remember how overuse of glyphosate herbicide in Roundup-resistant crops has brought about a number of glyphosate-resistant weeds?

A Kansas State University entomologist worries that overuse of Bt corn traits could have the same effect on corn rootworm. 

Jeff Whitworth alerted participants of a corn plot tour on Monday that the effectiveness of Bt hybrids against corn rootworm shows signs of breaking down this growing season. 

"I hate that. It means we're going to have to go back to in-furrow insecticide application, or chemical insecticide treatments," he says. 

Corn hybrids stacked with Bt traits are so prevalent that many farmers plant these hybrids even when it's not necessary. Also, growers are buying seeds already treated with insecticide and fungicide coatings, which has hastened the resistance problem. "I don't believe we need to use Bt corn unless we're planting continuous corn in the same field," he says. "We need to use these technologies judiciously, not just because we can."

Admittedly, it's hard to find hybrids that don't already contain Bt traits, or come with an insecticide coating already in place. Whitworth warns that growers should ask seed dealers for these naked hybrids and only plant them if the danger for corn rootworm is imminent.

KSU has yield trials around the state featuring corn hybrids without the Bt traits and without insecticide treatments. These plots only receive treatment if corn rootworm poses a problem. Yield results will be available after harvest, Whitworth says.

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