The Future of Dicamba

Dicamba Use Faces Trio of Threats: Courts, Weeds and Farmer Fatigue

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
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Weed control could look very different in 2021, depending on the legal availability of dicamba herbicides for postemergence use, farmers' seed decisions and evolving weed tolerance to the chemistry. Here's the latest on all three. (DTN photo by Jim Patrico)

ROCKVILLE, Md. (DTN) -- With 60 million acres of Xtend cotton and soybeans and rising herbicide-resistance problems across the crop spectrum, dicamba use in U.S. agriculture is at or near record heights this year.

Yet the chemical's future has never been less certain.

The most pressing question facing farmers and the industry is whether two companies, BASF and Bayer, will be able to get new registrations approved for XtendiMax and Engenia, two over-the-top dicamba herbicides whose registrations were vacated by the Ninth Circuit Court of Appeals in early June.

With no clear timeline from EPA on when it might make those decisions -- nor any information on what new labels would look like -- the Xtend cropping system is faced with uncertainty as farmers near the fall seed-buying season, with some opting to switch to other herbicide-tolerant platforms. "I like the weed control [of dicamba], but not the risk," as one southeast Michigan farmer, Raymond Simpkins, put it.

Weeds themselves are evolving as a threat to the technology, as well.

Some scientists and farmers in the South and Midwest are noting a decline in the efficacy of dicamba on key herbicide-resistant weeds, particularly Palmer amaranth and waterhemp.

"It's not a surprise," said University of Tennessee Extension weed scientist Larry Steckel, who has documented Palmer amaranth populations surviving labeled rates of dicamba and 2,4-D. "We've been using dicamba on almost every acre in Tennessee since 2001 as a burndown. We've been exposing Palmer amaranth to dicamba for a long time, at fairly low rates."

Despite these threats to the chemical's future, Bayer is doubling down on its dicamba-tolerant trait system. The company is expecting final import approval any day for its XtendFlex soybeans, which will tolerate dicamba, glyphosate and glufosinate, and are poised for a 2021 commercialization. Later in the decade, the company is aiming to commercialize both 4-way and 5-way herbicide-tolerant corn that includes dicamba tolerance. Bayer also licenses its dicamba-tolerant trait broadly to other seed companies.

"We remain 100% committed to the Xtend system and that includes our seeds, our traits and our herbicides," Alex Zenteno, Bayer dicamba product manager, told DTN. "We have not changed that stance."


When a trio of federal judges handed down their decision to vacate three dicamba registrations on June 3, they made the unusual decision to immediately issue a mandate, which legally ended the registrations of Xtendimax, Engenia and FeXapan that same day. (Syngenta's Tavium herbicide was not named in the decision). Within five days, EPA had issued cancellation orders for the three herbicides. The dicamba-tolerant Xtend trait, however, remains available for sale and planting, leaving growers with few legal options to treat Xtend acres next year.

Bayer and BASF have rushed to submit final data to the EPA for new registrations for their chemicals.

Bayer told DTN it has nearly completed all its data submissions to EPA supporting a new registration for XtendiMax. The company has also submitted a new tank additive for registration to EPA for use with the herbicide. Bayer's Zenteno described it as a "volatility-reducing agent."

BASF did not grant an interview to DTN on its registration efforts, and would only say in an emailed statement: "We have recently resubmitted the registration package for Engenia herbicide for EPA review that includes all relevant data needed by the agency to make a registration decision this fall."

The company added that it has also submitted for registration, "a combination product that includes dicamba and other active ingredients for over-the-top use on soybeans and cotton."

Corteva Agriscience, which owns a major competitive trait, 2,4-D-tolerant Enlist crops, licenses a dicamba formulation from Bayer, which it markets as FeXapan. In an emailed statement, Corteva told DTN that any future registration of FeXapan depends on a successful XtendiMax re-registration, but said it was "too early to speculate" on whether they would work to make FeXapan available in 2021.

Whether the three herbicides will be re-registered is only part of the 2021 dicamba equation, however. What those labels could look like is another critical question for farmers. A new registration for these dicamba herbicides would stand as EPA's third attempt to revise their labels, which already contain some of the most complex use instructions of any pesticide.

When the three federal appellate judges vacated the original registrations, they took EPA to task for not fully evaluating the risks of in-season dicamba use. They specifically mentioned widespread off-target movement, complicated labels that inspired non-compliance, anti-competitive seed buying decisions as farmers sought to protect themselves from drift, and tension and conflict among farmers and their neighbors over alleged injury. See more here:…

Any future labels would presumably have to solve all those issues to avoid a similar legal challenge in the future, scientists and farmers have noted. "I don't quite see how you could possibly issue new post-emergent use labels, and not run into the same problems," said Bob Hartzler, Iowa State University weed scientist, whose state is grappling with widespread off-target dicamba crop injury this summer.

"If you look at that court decision, it doesn't sound like dicamba has much of a leg to stand on for postemergence application," agreed Sheffield, Illinois, farmer Matt Foes. "Going forward, I think people are looking at it for early postemergence or burndown scenarios."

Bayer's Zenteno declined to speculate on whether any new XtendiMax label might be limited to pre-emergence use or contain additional use restrictions. "Ultimately, it will be up to EPA to address the [Ninth Circuit] Court's concerns," she said. "And we feel that with all the information we're submitting to EPA, they'll be able to address the concerns the court has brought up," she added.

Before the registrations were vacated in June, EPA officials had said they were aiming to make a re-registration decision on these herbicides by early fall, in time for farmers to buy seeds. It's not clear if that timeline still stands, as EPA did not respond to DTN's multiple requests for comments.


The existing formulations of dicamba are already poised to cost their registrants' hundreds of millions of dollars. Bayer and BASF are appealing a $325 million jury judgement for dicamba damage to a peach orchard in Missouri, and Bayer has proposed committing $400 million to settle dicamba injury claims from 2015 through 2020.

Not surprisingly, the industry is working behind the scenes on newer formulations that could someday replace the very products Bayer and BASF are currently fighting to keep.

For the past few years, Corteva has been quietly testing a novel dicamba formulation with a handful of university scientists, with the aim of lower volatility. The company has submitted the formulation, described in public academic presentations as a dicamba-choline product, to EPA for review for registration.

"We will not speculate on the timing of completion of that review, nor on potential commercialization plans," Corteva's statement to DTN said.

Bayer is also working on new dicamba formulations, Zenteno told DTN.

"We have several formulations at different stages of the pipeline," she said. "We do have some formulations already submitted with EPA, and others in product concept stages." But for the 2021 season, XtendiMax, along with the newly submitted tank additive product, is the only product Bayer aims to have available, she added.

Another potential volatility-reducing tank additive for use with dicamba herbicides is under development at the University of Arkansas. The compound, a formulation of potassium borate, is greatly reducing volatility of dicamba herbicides in field trials so far, university Extension weed scientist Jason Norsworthy told DTN.


Zenteno said Bayer experienced "an incredible outpouring of support" from members of the agricultural community for the dicamba-tolerant crop system after the court's ruling on June 3. Seven national commodity and ag trade groups, including the American Soybean Association, National Cotton Council and National Corn Growers Association, wrote letters of information and support to the court, known as amici curiae, defending EPA and the use of dicamba. Bayer also heard "a lot of need and support" from farmers for continued in-season dicamba use, Zenteno said.

In interviews with farmers, DTN found more mixed responses, with varying attitudes illustrating the stark disagreements over dicamba use that the Ninth Circuit Court highlighted in its decision.

"It really depends on who you talk to," pointed out Iowa State University field agronomist Meaghan Anderson. "There are farmers who believe we will not survive if we don't have dicamba available for post-emergent applications. And then there is the other group who have hundreds of acres of injured soybeans from field end to field end, and they're saying how can we survive with this technology out there?"

Some farmers told DTN the court decision was a relief in some ways, given the chemicals' four-year history of volatility risks.

"I'm glad to see dicamba exiting as a management option," said Mark Nowak, who grows corn and soybeans in Faribault County, Minnesota. "The dicamba drift that hit my field [this year] went a half a mile. That's too much risk for the industry to tolerate."

Some farmers are already planning on moving to other herbicide-tolerant platforms, given the court decision. "I'm afraid we've lost dicamba in cotton and beans for the near future," said Keith Peters, who grows corn, wheat and soybeans south of Columbus, Ohio. "I'm probably going to switch to Liberty[Link]."

Others were conflicted, even if they didn't like the way dicamba-tolerant technology had divided the industry.

"Part of me was happy they pulled the labels, because it was making it really difficult to be a good neighbor," explained Kyle Samp, who farms in Randolph County, Missouri. "But I'm pretty worried about how this affects the future not just for new chemistry but for existing chemistry. I've had to hoe beans in the past, and I would really like to avoid doing that in the future."

Samp's fear was echoed by many. Even in Canada, the sudden end to the three dicamba registrations -- which only applied to U.S. growers -- has farmers uneasy, said Ontario farmer Dan Petker. "We aren't sure how our pesticide registration agency will look at this," he noted. "Enlist E3 beans will fast become the norm if anything happens to dicamba here."

Some wonder if dicamba use in other crops will come under scrutiny. "They vacated the soybean labels; they might come after the corn labels next," said Illinois's Foes. "We're seeing increased use in corn recently and therefore, more damage from it."

For farmers who haven't seen many dicamba problems in their region, the court decision seems unfair and alarming. "If a court can cancel one label on a chemical we thought was okay, what are they going to do on some others that have more known issues or less public trust?" wondered Justin Honebrink, a farmer from Deer Creek, Minnesota. "It feels like this is just the beginning and we are going to have a lot more options being pulled out from under us just as we get ready to use them."

But others expressed confidence that companies will succeed with new registrations. "If I had to guess, I'd say dicamba will be re-registered," said Charles Williams, who farms near Crawfordsville, Arkansas, where dicamba use is banned after May 25. He's betting on Bayer's future traits, which will widen the post-emergence chemical options. "This year I'm growing some XtendFlex soybeans for increase," he said of Bayer's forthcoming 3-way herbicide-tolerant soybean stack.

And for some, their preferred soybean genetics still outweigh herbicide options. "While we plant Xtend beans, because that's where we believe some of the best genetics are, we do not spray dicamba -- it just isn't worth the risk," said Genny Haun, who farms near Kenton, Ohio. "So any decision regarding [registrations] does not have much of an impact on our operation."


As farmers fret and the EPA evaluates new dicamba registrations once again, scientists are finding that the target of these herbicides -- weeds -- are evolving in problematic ways.

This summer, many alleged dicamba drift cases are quickly turning into suspected resistance cases for Tennessee's Steckel. "It isn't hard to go from a dicamba drift case to fields nearby and see live and dead Palmer amaranth out there," he said. "It seems like they are recovering quicker from dicamba applications than ever before. Instead of taking two weeks, it's closer to 10 days before they start putting on two inches of growth a day again."

This spring, Steckel found that pigweed dicamba escapes collected in his state in 2019 could survive a labeled rate of dicamba herbicides. Now samples he sent to Texas Tech University are showing the ability to survive 2.5 times the labeled rate of dicamba.

"It is definitely translating to the field," he said. Some Tennessee cotton growers are finding that, even after burndown and preemergence herbicide use, they have to follow two postemergence dicamba applications in cotton fields with a third postemergence application of glufosinate in order to clean up weeds, with total weed control costs nearing $90 per acre, he said.

Farther north, weed scientists are watching waterhemp escapes with growing alarm.

Iowa State University weed scientist Prashant Jha did a survey of waterhemp populations from across Iowa in corn and soybean fields last year. Greenhouse tests show that some of the populations can survive labeled rates of both dicamba and 2,4-D.

When University of Missouri weed scientists evaluated waterhemp samples from four states this winter -- Illinois, Indiana, Missouri and Nebraska -- they found that 14% were able to survive a full rate of dicamba herbicides. For some of those waterhemp populations, even a second full rate of dicamba did not provide full control.

In Indiana, the pattern emerging is clear, said Purdue University Extension weed scientist Bill Johnson, who is seeing some waterhemp plants re-growing after dicamba sprays, especially when plants exceed label heights at application.

Up to two applications of dicamba are now required to control those populations. "These are populations we might have killed [with one spray] two years ago, and this year, we're not," he said.

Emily Unglesbee can be reached at

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Emily Unglesbee