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Scientists say EPA’s dicamba restrictions won’t be strong enough to stop crop damage

Sikeston farmer Trey Wilson said he saw substantial damage to his soybean crops this year. On the left is what a healthy soybean plant looks like; on the right is a soybean plant showing signs of dicamba damage.
Trey Wilson

Scientists are concerned that the Environmental Protection Agency’s recently announced limits on dicamba herbicide use will not be effective in preventing widespread crop damage.

The federal agency last week approved the use of dicamba-based herbicides, such as Bayer’s XtendiMax, until 2020. However, it noted several restrictions in attempts to curb the herbicide’s off-target movement that has ruined more than 1.1 million acres of soybeans in the United States this year

The new limits include prohibiting farmers from spraying the chemical on dicamba-tolerant soybeans 45 days after planting and on dicamba-tolerant cotton 60 days after planting.

Researchers say that this restriction won’t be effective, given that many farmers are likely to plant soybeans in late May and June. In Iowa, state agriculture officials received 90 percent of complaints about dicamba misuse after June 15, 2017.

It would make more sense to impose a date to stop dicamba use, since hot summer temperatures can cause dicamba to drift and damage crops in other fields, said Bob Hartzler, weed scientist at Iowa State University.

“It’s sort of frustrating that EPA had a teleconference with academic weed scientists asking what we felt would be appropriate measures, and not a single one of those is in the new label,” Hartzler said.

States are stricter

Missouri and other states heavily impacted by dicamba-related damage imposed stricter bans on the herbicide’s use. The Missouri Department of Agriculture this year required growers in the bootheel to stop applying dicamba after June 1, and after July 15 for the rest of the state.

As Hartzler wrote in a blog post last week, EPA’s other new restrictions don’t reflect what data has shown about dicamba-related damage. For example, the new label for dicamba requires that only certified applicators use the herbicide. Uncertified applicators were responsible for less than 40 percent of the misuse complaints reported to Iowa agriculture officials in 2017, Hartzler said.

“These numbers don’t suggest the classification of applicator has a big influence on the likelihood of off-target movement,” he wrote.


Bayer expects that farmers will plant an increase of 60 million acres of dicamba-resistant soybean and cotton in the 2019 growing season.

“Growers have indicated the need for this important tool, as a component of a complete weed-management system, to fight tough-to-control weeds,” Ryan Rubischko, Bayer’s dicamba portfolio lead, said in a statement. “[The EPA’s] continued registration, based on an extensive review, keeps this much-needed weed-control tool in the hands of growers.”

Farmers have also become concerned about dicamba’s impact on crops beyond soybeans. As NPR’s Dan Charles reported this fall, the chemical has also damaged cypress and sycamore trees in Tennessee and Arkansas.

“If the only thing at risk were soybean fields, then let agriculture do what it wants,” Hartzler said. “But when you start damaging native plants and trees, that, to me, is unacceptable.”

Follow Eli on Twitter: @StoriesByEli

Eli is the science and environment reporter at St. Louis Public Radio.