Experts concerned about dicamba overuse

Some agriculture experts fear old mistakes are being repeated as farmers rely more on the weed killer dicamba.

Dicamba has already caused damage to millions of acres in crop damage by drifting into fields of crops, such as cotton and soybean, that are not bioengineered to withstand it.

As farmers were facing increasing weed resistance to glyphosate, agrichemical company Monsanto introduced a new use for an older weed killer, known as dicamba, to help control weeds in soybean and cotton crops.

Dicamba has been used in corn and pastures for weed control since the 1960s, but the company described the 2016 product release as “the largest biotechnology launch in company history.”

“Today, herbicides play an important role in helping farmers control weeds, but if a weed control program is not sufficiently diverse, there is potential for the development of resistant populations,” said Charla Lord, spokeswoman for Bayer.

Dicamba is extremely volatile and prone to drift off target, damaging nearby trees, fields and other plants. Experts estimated dicamba caused damage to 3 million acres of crops in 2017, with continued damage in 2018.

“I think the wrong direction is substituting one more herbicide for one herbicide that no longer works anymore. That just gets us on the herbicide treadmill,” said Bill Curran, president-elect of the Weed Science Society of America and emeritus professor of weed science at Penn State University.

In 2016, an Arkansas farmer was shot and killed over a dispute with a neighbor on the use of dicamba.

Bayer bought Monsanto in 2018 and inherited dozens of lawsuits over the damages dicamba has caused to crops.

Aaron Hager, a University of Illinois weed scientist, said he believes the dicamba problem could have been prevented if weed resistance to the pesticide glyphosate had been better managed. Glyphosate is the key ingredient in Roundup and the most used pesticide in the Midwest.

“If glyphosate resistance had not evolved, I don’t think we would be entertaining dicamba at all,” said Hager.

While glyphosate replaced other pesticides in the late 1990s and early 2000s, Hager said the answer to the growing weed resistance was to add more pesticides on top of glyphosate.

Sarah Ward, associate professor of plant genetics at Colorado State University said after glyphosate’s success, research and development for new herbicides fell off as well.

“There was a long period where there were no new herbicides,” she said. “I think everyone thought glyphosate had it sewn up.”

Reliance on glysophate hampered research

Curran said Roundup’s dominance in the marketplace, along with industry consolidation such as the merger between Bayer and Monsanto, really hurt research into new products.

“The thought was, ‘glyphosate is the answer. It’s going to take care of our weeds.’ So the need for new herbicide technology sort of died,” he said. “Some of these (research and development) programs from some of the major companies just started to shrink.”

Just like Roundup, dicamba users are now seeing signs of weed resistance as well, said Curran. He said the U.S. Environmental Protection Agency, which regulates pesticides, could be doing more to prevent weed resistance.

“They should have required limitations on the frequency of use of these technologies,” he said. “If the farmer has the ability to use that technology, and those associated products every year, in the same field, whether it’s dicamba or whether it’s glyphosate or whether it’s other herbicides, it’s destined for failure.”

Hager said the only way to ensure weeds don’t develop new resistances is to remove all weed seeds from the field at the end of the year. If they can’t spread new seeds, they can’t form new resistances.

“If we go down the same road with this (dicamba) as we do with Roundup, why would we think the evolutionary process is any different?” said Hager.

Dane Bowers, technical product lead for herbicides at Syngenta, said Syngenta recommends applying multiple herbicides that attack weeds differently, to ensure even resistant plants are killed.

“Additionally, we need to begin utilizing non-herbicidal means of weed control. Things like cover crops, more tillage, where we won’t lose soil,” he said. “Mother nature has a way of overcoming any practice we implement. That is why we come at this from multiple angles.”

Cover crops help

Iowa farmer Jack Boyer has been using cover crops on his farm for more than a decade. He said the first year he planted cover crops, he saw immediate benefits.

“I had no yield hit and avoided some chemical sprays. That really reduced my weed pressure,” Boyer said.

He said cover crops not only decreased the amount of pesticides he’s had to apply, they return nutrients to the soil, which improves his crop.

“With being a century farm, it had degraded its organic matter over the years to where it was roughly half of what it was in its prairie days,” Boyer said. “Now I’ve turned that around, and I’m increasing the organic matter. That’s a big deal.”

Lord said glyphosate can help implement other non-chemical weed management solutions.

“Glyphosate also simplifies adoption of cover crops by providing a simple, non-mechanical means to eliminate the cover crop prior to planting the cash crop,” Lord said.

Ward said she worries the industry is just repeating the same mistakes as it did with glyphosate.

“I think dicamba is a lot more troubling,” she said, pointing to the chemical’s resistance, but also the issues of off-target movement and damage to vulnerable plants. “This is not a good response to dealing with glyphosate resistance.”