ROCKVILLE, Md. (DTN) -- With no new herbicide modes of action on the horizon, agrichemical companies are combing through the archives for options to battle herbicide-resistant weeds.

Now, for Bayer Crop Science, that rummaging might be about to pay off.

"We looked under every stone -- all our existing molecules -- to see what we had missed," explained Frank Rittemann, who manages Bayer's portfolio of selective herbicides in corn, soybean and cotton in North America. "And that's how we came across diflufenican, which is a molecule with a very successful history in Europe as part of our cereal herbicide offerings."

Bayer is now working on bringing this selective broadleaf herbicide across the ocean, to U.S. and Canadian corn and soybean farmers, with a primary aim of helping tackle pigweed species such as waterhemp and Palmer amaranth, which are rapidly outpacing herbicide control options. Pending regulatory approval, the company hopes it will be commercially available for pre-plant and preemergence applications in the mid-2020s.

"It's no big secret that, particularly in soybeans, getting control of resistant weeds is an ever-increasing challenge," Rittemann noted.

Most recently, weed scientists have uncovered Palmer amaranth populations with six-way resistance to herbicides and waterhemp populations with seven-way resistance. Even relatively recent herbicide-tolerant weed platforms, such as Xtend and Enlist, are running quickly into the problem, with Palmer amaranth developing resistance to dicamba and glufosinate in the past two years, with 2,4-D-resistance likely, as well. (See more here: https://www.dtnpf.com/… and here: https://www.dtnpf.com/…). Even more concerning is the growing incidence of metabolic resistance, wherein weeds learn to escape control by rapidly metabolizing herbicides -- even ones they have never encountered.

Diflufenican is a Group 12 herbicide, a pigment inhibitor with residual activity. Although not a new mode of action globally, this class of herbicides is not currently in use in corn and soybean fields in the U.S., Rittemann said. Bayer's internal testing showed good activity against the pigweed species, he said. "Palmer amaranth and waterhemp are key strength areas of this molecule," he said. "Once we found that match, we were very interested in bringing this molecule to North America." So far, the herbicide has not been widely available to academic scientists for testing in the U.S., but Rittemann said Bayer hopes to expand access it in the next couple years. The mid-decade commercialization timeframe gives Bayer "ample time to continue to test this," he said. "Part of that will involve broader testing with universities."

The chemical will be marketed as Convintro in soybeans. In an effort to protect its efficacy, Bayer will sell it within premixes, Rittemann said. The first such offering will contain diflufenican, plus metribuzin (Group 5) and flufenacet (Group 15). It will be positioned as a pre-plant and preemergence option, to clean up fields before the crop gets underway. "If we can provide a layer of residual control that prevents weeds from ever emerging, that's best, because once they emerge, they immediately put pressure on a crop," Rittemann said. "But you will still need to come back with other molecules."

Similar products will be offered in the corn herbicide market, possibly under a different brand name, Rittemann added. Bayer is also looking to expand its availability to other crops in the future.

But first the herbicide must make it through EPA's regulatory review, a process that can take up to two years. Based on that timeline, Bayer is targeting a commercial launch of Convintro in the mid-2020s. The herbicide has also been submitted to Canada's Pest Management Regulatory Agency (PMRA), with a similar timeline.

Bayer already offers diflufenican in Europe, where it underpins many herbicide premixes for pre and postemergence use in wheat and barley, such as Alternator Met, Giddo, Hamlet, Liberator, Octavian Met, Othello, Proclus and Regatta. As a result, the chemical has already cleared regulatory approvals in the EU, and Bayer has production capacity for it in place, both of which could help speed its entry into the North American market, Rittemann added.

"We have an existing production footprint in Europe, so we know how to produce it efficiently and economically," he said.

See more on Bayer's announcement on this herbicide here: https://www.bayer.com/….

See UK-based herbicides with this active ingredient here: https://cropscience.bayer.co.uk/….

Emily Unglesbee can be reached at Emily.unglesbee@dtn.com

Follow her on Twitter @Emily_Unglesbee

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