Dow-DuPont’s modified corn fails to control pest, scientists say

A type of corn marketed by Dow Chemical Co. and DuPont Co. is failing to live up to promises that it prevents a damaging worm from feeding on the crop, according to a group of insect experts.

Corn containing the Herculex trait isn’t controlling the western bean cutworm, six entomologists from Michigan, Indiana, Ohio, New York and Pennsylvania wrote in an " open letter to the seed industry" posted on the website of Purdue University. The scientists urged seed companies to stop labeling Herculex for control of the pest so farmers won’t be lulled into a false sense of security.

"People are frustrated and angry and, more importantly, yield was lost," they wrote in Purdue’s latest Pest & Crop Newsletter. "Before growers make seed choices for 2017, we again urge the seed industry to acknowledge the reality of what is happening in the field."

DuPont cut the efficacy rating of Herculex on western bean cutworms to " moderate" in its 2017 Product Use Guide, from "very good" in the current-year publication. The change was made before the company was aware of the scientists’ letter, according to spokeswoman Sharly Sauer.

Larger insect infestations and "reduced sensitivity" to the bug-killing trait have recently increased corn damage, Dow said Wednesday in an email. Farmers need to take additional steps to control cutworms, including potentially spraying insecticides, DuPont and Dow said separately.

DuPont and Dow Chemical—the parent of Indianapolis-based Dow AgroSciences—are in the middle of a $59 billion merger that is expect to close this year.

In a written statement, DowAgro said it "empathizes with growers that are experiencing difficulty in controlling outbreaks of Western Bean Cutworm," and that it was prepared to provide customers "additional guidance for the 2017 growing season in line with the recommendations from university experts."

For Herculex to work against the cutworms, the pests need to digest a certain amount of the treated corn tissue, DowAgro said. In areas with large populations of cutworms that have built up some tolerance to the product, that can result in "some level of observable ear damage."

"Under such challenging circumstances, protection of corn from this pest will require additional management practices," the company said.

Other genetically modified crops have lost some effectiveness after years of use. The root-chomping western corn rootworm has been showing signs of resistance to Monsanto Co.’s YieldGard corn for years. It’s one of five major crop pests known to have overcome insecticides produced by engineered corn and cotton. These crops produce insecticidal proteins derived from Bacillus thuringiensis, or Bt, a soil bacterium, that can replace chemical insecticides. The problematic Bt protein in Herculex is called Cry1F.

"Cry1F has failed in our states," the entomologists wrote. "For growers in our states, the costs of scouting and spraying Cry1F corn negates a major reason they purchased and planted a hybrid with the trait in the first place."

The scientists investigated the efficacy of the trait amid “dozens of phone calls and e-mails,” they said.

Western bean cutworms feed on corn kernels. Untreated, they can lead to the growth of fungus and elevated levels of hazardous mycotoxins. Herculex is marketed for protection against eight other insects.

Also failing are Monsanto’s Roundup Ready crops, engineered to tolerate sprays of Roundup weedkiller. To combat an increasing number of weeds no longer killed by Roundup, the company has developed crops that also tolerate dicamba herbicide, while Dow has created competing technology based on the weedkiller 2,4-D.

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