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Dicamba revisited – Will corn be the next herbicide debacle?

Published by FernsAG Insider

By Liza Gross

April 30, 2019

Dicamba-tolerant corn seeds aren’t available yet. But if the seeds reach the market, and tens of millions more acres are sprayed with the herbicide, some scientists expect a repeat of the soybean disaster, in which the highly volatile weedkiller drifted off-target and damaged 5 million acres of conventional soybeans and an untold number of other crops.

In March, the EPA announced it was considering new uses of dicamba on corn engineered by Monsanto (now owned by Bayer), raising concern that the herbicide might be sprayed later in the growing season and spread to crops without genetically-modified resistance.

The company first got approval for its dicamba-tolerant corn seeds in March 2016, a month after executives met with top EPA officials to figure out a “defensible approach” to the “volatility” problem—dicamba’s inherent tendency to drift off target and damage nearby crops and wild plants.

As FERN and Reveal reported last November, the EPA had ignored scientists’ warnings that spraying dicamba on millions of acres of soybeans would endanger scores of vulnerable cultivated and wild plants—which is exactly what happened. It created a flash point for conflict in farm country.

Now, the EPA may allow farmers to spray dicamba on some 90 million acres of corn — the nation’s most widely planted crop. Although corn is not as sensitive to the herbicide as soybeans, it still the raises the prospect that the damage would spread even further to non-targeted crops.

That prospect worries Aaron Hager, a weed scientist at the University of Illinois, who says that conventional corn is not as tolerant of dicamba as many assume. The idea that you can spray dicamba on corn at any growth stage without harming it is wrong, Hager says.

He recalls the time, as a young graduate student, he asked his adviser where he could find research on late-season exposure to dicamba. “He looked at me and said, ‘I have no idea.’ Well, I got to thinking about it and it made perfect sense. Why would anyone in their right mind ever look at dicamba drift on pollinating corn? We’d never had that use pattern before.”

Years ago, Hager says, farmers weren’t as reliant on chemicals to control weeds, partly because the chemicals were more costly. When they did spray chemicals like dicamba on corn, it was mostly before planting or on early-stage corn, when the plants could tolerate it. “Us old-timers used to say, if the corn’s taller than a soda can, stop,” he says. “Everybody knew that you didn’t spray big corn with dicamba.”

And because corn was always planted early in the season—before farmers put in soybeans, which are highly sensitive to dicamba, and before vulnerable wild plants had leafed out—the volatile weedkiller posed minimal risks. That all changed starting in the late 1990s with the new “total post-emergence systems,” Hager says. Herbicide-tolerant crops allowed farmers to spray chemicals to kill weeds long after crops sprouted, wreaking havoc on those plants without the built-in protections.

It’s impossible to predict what restrictions the EPA will place on the herbicide. If the agency allows spraying later in the season, Hager says, corn farmers will face the same conditions that have caused so many problems with soybeans—high temperatures that favor volatility—leading the herbicide to drift far beyond its target crop.

That means that corn farmers who don’t buy the new tolerant seeds might find themselves in the same boat as soybean farmers, who saw some 5 million acres of conventional soybeans damaged after the release of dicamba-resistant soybeans.

Soybean farmers responded by buying dicamba-tolerant soybeans out of self-defense, something that corn farmers may end up doing as well. “But unfortunately, we have lots of other dicot species in our landscape, like trees,” Hager says. Dicots, or broadleaf plants like soybeans, most garden vegetables and trees, are especially sensitive to dicamba.

Last year the Illinois Department of Agriculture saw a 35-percent uptick in official complaints of damage from dicamba drift, which underestimate the true damage because many farmers don’t bother to file a complaint. A fruit grower in southern Illinois told a local TV outlet that dicamba damaged hundreds of his peach trees, even though his orchard is nestled in the hills far from row crops.

The damage will continue as long as the EPA fails to address the volatility problem, Hager says. People spraying the chemical can do everything in their power to adhere to the requirements on the label, “but if you’ve got a product that changes from a liquid to a gas in the leaves, there’s nothing that applicator can do to stop that.”

Even if farmers could keep dicamba where they spray it, it’s only a matter of time before evolution prevails and the weeds develop a resistance to the chemical. In March, Hager reported that farmers’ most feared nemesis has outwitted yet another class of herbicides.

Waterhemp, a member of the wildly prolific pigweed family, no longer responds to so-called Group 15 herbicides in what Hager described as the first case of resistance to these chemicals in a broadleaf plant. The news couldn’t be worse for farmers already struggling to contain a weed that Hager says has evolved resistance to more types of herbicides than any other weed species in Illinois. Just two chemicals still thwart waterhemp, according to a study published last year: dicamba and glufosinate.

Any hope of overcoming this “resistance treadmill” lies in taking a more holistic approach to managing weeds, starting with seeds in the soil, Hager says. It’s a message he’s preached for a quarter century. “Yet every new instance of resistance we see further emphasizes that I have failed with that message. What we do know for sure is that nature is going to win. We’re not going to win.”

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Dicamba Drift Lawyers at Peiffer Wolf Carr & Kane and Arkansas attorneys Michael Smith and Paul James are fighting on behalf of farmers and landowners to seek maximum compensation for the damages suffered due to Dicamba. If you suspect that your crops or plants have been damaged by dicamba, contact Peiffer Wolf Carr & Kane by filling out a Contact Form or by calling 314-833-4826 for a FREE Consultation.

Also, you can reach Paul Lesko directly at 314-833-4826 or at [email protected].