Sorghum Herbicide Advances

Herbicide-Tolerant Sorghum Finally at Hand

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
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Herbicide-tolerant technology is within sorghum growers' grasp now that the EPA has approved the active ingredient in DuPont's Zest herbicide, designed to be sprayed over top of Inzen grain sorghum. (DTN photo by Emily Unglesbee)

ROCKVILLE, Md. (DTN) -- Sorghum growers' decade-long wait for herbicide-tolerant technology is finally nearing an end.

The EPA has approved the active ingredient for DuPont's Zest herbicide, a key component of the ALS-tolerant Inzen grain sorghum system.

The agency announced its registration approval for nicosulfuron use in sorghum, which will eventually be marketed as Zest, said Wayne Schumacher, the commercialization manager for DuPont's Crop Protection division. The EPA is expected to approve the official Zest brand label as early as April, he added.

The Zest herbicide is designed to be used over the top of Inzen grain sorghum hybrids, which have been bred to tolerate it. Two companies have licensed the Inzen trait -- DuPont Pioneer and Advanta Seeds.

This spring, Advanta will release one Inzen hybrid under its Alta Seeds brand to 50 to 75 farmers to grow "large-scale commercial plots" in Kansas and Texas under careful stewardship, said Brad Holzworth, director of marketing for Advanta Seeds. By 2017, the company hopes to do a full commercial launch of two additional Inzen hybrids, he added.

Pioneer has two Inzen grain hybrids in field trials in 2016, an ultra-early maturity and a mid-to-early maturity, said Liesel Flansburg, Pioneer's North America brand manager for grain sorghum. "If they yield and perform as we hope, they will go into more extensive in-field trials in 2017, with a potential 2018 commercial launch," she told DTN. The company also has more than 200 experimental hybrids with the Inzen trait in the pipeline, she added.

This technology will be a boon to sorghum growers, noted Justin Weinheimer, the U.S. Sorghum Checkoff's crop improvement director. Sorghum is closely related to the grass weeds that infest it, so growers have never had post-emergence grass control options.

As a result, herbicide-tolerant technology has been the "number one priority of the sorghum industry," Weinheimer said.

The Inzen trait was first developed through traditional breeding by Kansas State researchers and licensed to DuPont in 2007, which in turn licensed it to Advanta Seeds. Since then, both companies have been working to get sorghum hybrids with the Inzen trait up to commercial yield and performance standards.

An herbicide-tolerant sorghum system comes with risks, however. The close genetic relationship between sorghum and grass weeds means the potential for weeds to develop resistance to the Zest herbicide will be very high. The gene that researchers used to make Inzen tolerant to ALS herbicides actually originated from a weed, namely populations of ALS-resistant shattercane, a close relative of grain sorghum.

DuPont has crafted label requirements to delay weed resistance in light of this, Schumacher said. Growers who use Inzen grain sorghum will not be allowed to double crop sorghum after it, a practice that would give any weeds that survived the Zest herbicide another season to grow and spread.

Schumacher said the company worked closely with weed resistance models from the University of Nebraska to create this label restriction. "If we allow this double cropping, the models show that we could accelerate weed resistance very quickly," he said.

Taking double cropping off the table is unlikely to discourage many sorghum growers, Weinheimer said.

"Most commercial grain sorghum growers are actively involved in some type of crop rotation, so we don't see that specific stewardship protocol as a major hurdle," he said. "In fact, I think it will fit very nicely into current sorghum management practices."

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Emily Unglesbee