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Take Action efforts expand to Bt corn insecticide resistance

ST. LOUIS, Mo. — Take Action, an initiative founded by the soy checkoff to combat pesticide resistance, is expanding to promote practices that can counter potential insecticide resistance, especially in Bt corn.

The National Corn Growers Assoc. (NCGA) announced the program expansion in December.

“Now is the time to take action before insects become resistant to Bt technology like weeds have become resistant to herbicides,” said Don Duvall, a farmer from Carmi, Ill., who chairs the NCGA Freedom to Operate action team.

The program advocates planting a proper refuge; rotating crops, traits and insecticide modes of action; and in-season crop scouting to spot potential resistance problems.

“Those three steps – the proper refuge, rotation of many kinds, then scouting in-season to determine the effectiveness – has been the format they’re taking with Take Action in hopes of keeping this technology viable for more years,” said Duvall.

The Eastern Corn Belt is on the fringe of corn rootworm resistance, which hits hardest in Illinois, Iowa, Missouri, Nebraska and Kansas. Warning signs of possible Bt resistance include poor pollination from large number of beetles in the field that may be leaf-feeding and damaging silks.

“Growers should be looking for corn rootworm in areas where we haven’t had a lot of rootworm issues, and other secondary pests,” said Chris DiFonzo, Michigan State University extension entomologist. “In the South, there are other pests they are concerned about, like armyworm and earworm, chewing through some of these (Bt) products.”

DiFonzo in December published the 2018 BT Trait Table to help producers keep track of corn traits, efficacy and refuge requirements. The online resource is hosted by Texas A&M University at

Although corn rootworm is not a major pest concern in Michigan, according to DiFonzo, resistance is being documented in a key pest in Ohio, Michigan and Ontario. “What we have had is western bean cutworm,” she said. Companies have removed WBC from the Cry1F Bt protein.

“I think there’s very good data from Ontario which shows there’s (WBC) resistance now,” said DiFonzo. “When you don’t get good kill, you create a population which eventually becomes full-blown resistant. In the northern tier here, where western bean cutworm is our major pest, they need to be scouting and spraying for that pest. There should be no claim of control for western bean for Cry1F anywhere.”

The potential for insect resistance underscores the importance of in-season crop scouting. “We’ve always just said that scouting is so critical,” she said. “And I think maybe, with Roundup Ready and Bt, we had a decade of laziness in a way, where those traits were very effective and you felt like you almost didn’t have to scout.

“But I think we’re turning the clock back to have to (when we’re scouting) either manage the pest with insecticides, or we’re looking for trouble – we’re looking for things that are failing. Part of the scouting is just seeing if there is the efficacy that you expect there.”

Duvall agreed that scouting is all the more important in today’s production environment. “The effectiveness of the traits that we have can lead to a sense of complacency,” he said. “I will admit that perhaps it is easy to forgo that scouting because it has been so effective in the past that maybe there’s less of a sense of urgency.”

But doing the proper scouting – and the other resistance management steps recommended by the Take Action campaign and other educators – will only pay off for producers, according to Duvall. “The most important part is the economic advantage Bt provides for us. There’s the greater yield.”

But there is also a quality of life argument for maintaining the efficacy of Bt traits for insect control, said Duvall. “There’s also the quality of harvest aspect for us. It’s a lot less stressful to harvest corn that’s standing,” he noted.

The Take Action initiative encourages growers to follow recommended insect resistance management (IRM) strategies when planting corn and cotton with Bt traits. Planting the required insect refuge, mandated under EPA regulations for Bt variety use, is one of the most important strategies, according to NCGA.

Corn refuge requirements are 5 or 20 percent, and cotton refuge requirements are 20 or 50 percent. More information is available from the NCGA and at