Dicamba was supposed to solve farmers’ weed problems – instead it makes it harder for many

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In October, I was a guest on a podcast to discuss my recently published book, “Seed Money: Monsanto’s Past and Our Food Future,” which examines the agribusiness giant’s influence on the global food system.

After the show, I received many calls from all over the world, but only one really stood out to me: a farmer talking on his cell phone from the seat of his combine harvester while harvesting soybeans.

Farmers don’t like stopping tractors on good weather days in the fall, but it was important. The caller meant a chemical weedkiller called dicamba that had been sprayed on nearby fields. He claimed it was damaging his crops. And he was not alone.


In 2021, thousands of U.S. growers reported to the Environmental Protection Agency that dicamba sprayed by other farmers — sometimes up to a mile and a half away — was damaging crops in their fields. Complaints came from all over the country.

The list of plants affected was staggering: sycamores, oaks and elms; azaleas, black-eyed and pink-eyed Susans; garden tomatoes, peppers and peas. According to an EPA memorandum, there were 2,700 “dicamba incidents,” affecting about 3.6 million acres, in 2017. Two years later, the number of incidents rose to 3,300.

This problem has been accumulating for more than five years, and the EPA acknowledges that the modest controls it needs, such as creating buffer zones around fields, are not working. But tighter restrictions on dicamba use aren’t likely until the 2022 growing season, as they would require a complicated legal process.

Why is it so difficult to solve this national problem? To answer this question, we have to go back to 1996, when a revolution transformed American agriculture.

From Roundup to dicamba

Weeds have always been a costly headache for farmers. A 2016 study estimated that if left unchecked, weeds would roughly halve corn and soybean yields in North America, causing $43 billion in annual economic losses for these two crops alone. One of the problems farmers face is that weeds are good at developing resistance to the chemicals used to kill them, so herbicides lose their effectiveness over time.

Weed problems became particularly serious in the late 1980s and early 1990s as widely used herbicides called ALS inhibitors became less and less effective. That’s why farmers were excited about Monsanto’s “Roundup Ready” crops, first introduced in 1996.

These plants were designed to withstand heavy sprays of Monsanto’s flagship herbicide, Roundup. Monsanto had developed and patented glyphosate, the active ingredient in Roundup, in the 1970s, but the advent of Roundup Ready seeds caused glyphosate sales to skyrocket.

It seemed like a magic system: farmers could treat fields with glyphosate throughout the growing season without harming their crops. For a few years, overall herbicide use plummeted: farmers used glyphosate in large quantities, but stopped buying most other herbicides.

Glyphosate use has increased significantly since the introduction of Roundup Ready seeds from 1996 (move the slider to compare 1995 and 2019 use). Monsanto claimed that this approach would make agriculture more sustainable by reducing the long-term use of herbicides and pesticides – especially older ones. , more toxic brands.

Soon, however, the system began to falter.

In the early 2000s, scientists began reporting that weeds were developing resistance to Roundup. In response, Monsanto rolled out a new generation of genetically modified seeds that would make crops resistant to a wider range of older herbicides. Farmers could use these older products with Roundup, improving their chances of killing most weeds.

One of the chemicals Monsanto bet on was dicamba, first introduced in the 1960s. In 2015 and 2016, the company began producing “Roundup Ready Xtend” brand seeds that were designed to tolerate heavy sprays of dicamba and glyphosate. The logic was that the dicamba would kill glyphosate resistant weeds and the glyphosate would kill any other unwanted vegetation.

The solution becomes a problem

It quickly became apparent that this patch was seriously flawed. Dicamba is one of the most volatile herbicides on the market, which means it easily changes from a liquid to a vapor at warm temperatures. When farmers sprayed dicamba in hot weather, it tended to vaporize and drift off target, spreading to fields and farms that were often not planted with crops genetically modified to tolerate it.

The farmer who called me from his combine was harvesting organic soybeans that did not contain Monsanto’s Xtend traits.

Maddeningly for farmers, Monsanto had seen this coming. In a 2020 federal court case, Bader Farms v. Monsanto, confidential company documents revealed that the company was aware that dicamba sprayed on Xtend crops would likely drift off the target. Monsanto sales reps even called it an outlet for dicamba-tolerant seeds. “Press your neighbor’s protection,” a slide from an internal business presentation from 2013 suggested.

Farmers began complaining about dicamba drift soon after Monsanto introduced its first Xtend seeds. The Trump administration has ordered farmers not to spray dicamba in buffer zones around fields and to limit dicamba application to particular times of day, but it has had little effect.

Amid this controversy, the EPA extended approval in 2018 for three dicamba-based herbicides. But the U.S. Ninth Circuit Court of Appeals reversed that decision in June 2020, ruling that the agency ignored or downplayed evidence of dicamba harm and failed to consider how its licensed use would “rip apart the social fabric of farming communities”. In response, the EPA approved new dicamba licenses with a few additional control measures that it said addressed the court’s concerns.

A chemical arms race

Now the Biden administration is considering how to deal with the dicamba — and not too soon. Farmers reportedly saw weeds that developed resistance to dicamba and other herbicides recommended for use with a new generation of genetically modified seeds.

According to weed specialists, this happens precisely because farmers use such high amounts of these chemicals during the growing season.

Seed companies like Germany’s Bayer, which now owns Monsanto’s product portfolio, say one solution is for farmers to buy seeds that can tolerate a wider range of weedkillers. Recently, for example, Bayer sought approval for a new line of seeds that would make crops resistant to five different types of herbicides.

For farmers, this will mean greater reliance on a growing range of petrochemicals, and therefore higher costs. Today, American farmers use more than twice as many herbicides to grow soybeans as before the introduction of Roundup Ready crops.

The dicamba drift can be seen as a symptom of greater petrochemical dependency that threatens the viability of the US food system. Research in this area clearly shows that if federal agencies are serious about helping farmers solve weed problems, they would do well to turn to agricultural innovators who demonstrate that crops can be grown productively and profitably without depending as many synthetic pesticides.

In the United States and around the world, farmers are looking for alternative ways to control weeds. Some are diversifying what they grow, using age-old practices like cover cropping, and seeking innovative methods from a burgeoning regenerative agriculture movement.

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