The Environmental Protection Agency announced Friday that it will let farmers keep spraying the weedkilling chemical dicamba on Monsanto's new dicamba-tolerant soybeans and cotton. The decision is a victory for the biotech giant and the farmers who want to use the company's newest weedkilling technology.

Farmers across the Midwest and Mid-South have been waiting for the EPA's decision for months ever since it became clear that dicamba was drifting into thousands of fields where it didn't belong and damaging those crops. Some groups have called on the EPA to ban the most troublesome uses of dicamba, following the lead of regulators in Arkansas.

The EPA, however, decided that the problems that occurred this past summer can be solved simply by adding a few new restrictions on how dicamba is used. In the future, applying dicamba will require special training; it can't be applied if the wind speed is greater than 10 mph and farmers will be asked to pay more attention to the risk that dicamba spraying may pose to nearby orchards and vegetable fields.

Farmers have used dicamba for decades, but this past summer, they got permission to use it in a new way, spraying it over the top of soybean and cotton crops that Monsanto has genetically modified to tolerate the chemical. This meant that more dicamba was sprayed, and it was being applied in the heat of summer, which makes chemicals more likely to turn into a vapor and drift.

Scott Partridge, Monsanto's vice president of global strategy, welcomed the EPA's decision. "We're very excited about it," he said. "It directly addresses what we found to be the causes of the off-target movement in 2017, and we think it sets the stage for all growers and applicators to have a positive experience in 2018."

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With this green light from the EPA, farmers are expected to plant even more dicamba-tolerant soybeans next summer. According to Partridge, farmers planted about 20 million acres of dicamba-tolerant soybeans this summer. He expects that number to double next year.

"The demand for it is overwhelming," Partridge says. "The need to control these difficult-to-manage weeds is huge."

The new restrictions on dicamba use, however, do not appear to address the problem of "volatilization" — when dicamba evaporates from soil or plants where it was sprayed and drifts in unpredictable directions. Many independent scientists say that this vapor drift was a major cause of damage to neighboring fields this summer.

Last year, Missouri did impose most of the restrictions that the EPA is set to require, and farmers in the state still saw widespread damage from drifting dicamba.

Bob Scott, a weed scientist at the University of Arkansas, recently showed me some experiments that he and his colleagues conducted. They sprayed trays of soil with dicamba, then placed those trays in a field of soybeans far from any dicamba spraying. The soybean plants next to the dicamba-treated soil showed clear signs of exposure to the chemical.

"We had a lot of volatility in these trials, a lot of movement" in unpredictable directions, Scott says. It wasn't what they were hoping to see, Scott says, but the results "do help explain why we had 966 complaints in our state."

In fact, fear of dicamba drift from neighboring farms may persuade some farmers to buy Monsanto's dicamba-tolerant seeds next year because those soybeans won't be vulnerable to windblown dicamba.

Brent Henderson, who farms near Weona, Ark., is one of those farmers. "If it's going to be legal to use and neighbors are planting it, I'm going to have to plant [dicamba-tolerant soybeans] to protect myself," he says. "It's very annoying. It's a property rights issue. My neighbor should not dictate what I do on my farm."

Partridge, the Monsanto executive, continues to insist that vapor drift was not responsible for any of the damage that farmers saw this past summer. And he also does not believe that farmers are buying dicamba-tolerant soybeans to defend themselves.

"When I talk to growers and ask them why they are deciding to buy our dicamba-tolerant Xtendimax seeds, they say it's because it's the highest-yielding seed out there," he says.

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