By vast

Published: December 6, 2018

Category: GMO News, The Organic & Non-GMO Report Newsletter

Proponents of genetically engineered crops often point to Bt insect resistant corn as a success in reducing pesticide use. That claim is now eroding as the devastating pest, western corn rootworm, is increasingly developing resistance to Bt corn including “pyramided” Bt corn hybrids.

This past October, Corteva Agriscience informed the U.S. Environmental Protection Agency that the company has confirmed resistance to the genetically modified trait Cry34/35Ab1 (Herculex RW) in rootworm populations in the northeastern Iowa county of Delaware.

Corteva claimed this was the first case of such resistance to its GMO trait. But Aaron Gassmann, an entomologist at Iowa State University, documented low levels of rootworm resistance to this same trait in Iowa in 2016. Gassmann described the resistance as “an early warning” for industry and farmers to improve their stewardship of the technology—or risk losing it soon.

Unfortunately, the warnings weren’t heeded. There were no major changes to management of Bt corn by farmers and industry, and the resistance problem has only gotten worse.

Cry34/35Ab1 forms the basis of many popular pyramided Bt corn hybrids, which offer multiple belowground GMO Bt traits targeting the rootworm. But the other two Bt traits in those pyramids, Cry3Bb1 and mCry3A, are already compromised by resistant rootworm populations. Cry34/35Ab1 has been the only effective Bt trait remaining in many cornfields in intensive corn-producing states like Iowa for several years now. Now that trait is being compromised, which could lead to farmers using more insecticides.

“There is so much pressure being put on that trait in Iowa,” said Evan Sivesind, program manager for the Iowa Pest Resistance Management Program, in an interview with Progressive Farmer. “It is really what is being leaned on by anyone who grows Bt corn here.”

Source: Progressive Farmer

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