Special Report: Glyphosate Research: alarming or alarmist?

Glyphosate use has soared in North America, Australia and South America since the advent of Roundup Ready crops. 


Companies have told me that ‘we’re no longer looking for something like Roundup …. We’re looking for something that will complement glyphosate … but not replace it completely.’

Francois Tardif 


On Jan. 17, 2011, Don Huber, a retired Purdue University professor, submitted a letter to U.S. agriculture secretary Tom Vilsack.

The letter did not go unnoticed.

Biotech corporations, university agricultural departments and countless bloggers immediately crucified or praised Huber’s assertion that a new, unidentified pathogen was putting the entire U.S. agricultural sector in jeopardy.

In the letter, Huber, a highly regarded plant pathologist, warned the pathogen was causing spontaneous abortions in livestock, triggering disease in soybeans and corn and could cause a “significant disruption of domestic food and feed supplies.”

Huber said the pathogen existed in higher concentrations in Roundup Ready crops, and he suspected glyphosate was to blame.

“It is well documented that glyphosate promotes soil pathogens and is already implicated with the increase of more than 40 plant diseases,” said Huber.

“It is urgent to examine whether the side-effects of glyphosate use may have facilitated the growth of this pathogen, or allowed it to cause greater harm to weakened plant and animal hosts.”

Nearly three years later, Huber’s critique of glyphosate still divides the agriculture community. Scientists at major U.S. universities, including Purdue, where he is professor emeritus, have dismissed his claims as unsubstantiated. On the other side, anti-genetic modification advocates and a minority of agricultural scientists maintain his warning was justified.

Charles Benbrook, program leader of a sustainable agriculture program at Washington State University, said there is little debate about the credentials of Huber, a retired colonel who specialized in natural and man-made biological threats.

Still, the letter was a mistake, Benbrook said.

“(To) say the theatre is burning down, we have to get everybody out of the theatre, you only get to do that once or twice,” said Benbrook, former chief scientist for the Organic Center, which provides evidence based information on the benefits of organic food.

“I don’t know if Don regrets doing it, but I sure regret that he did it. It undermined the confidence in and importance of most of (his) science that has stood up.”

At the time, the USDA was weighing the approval of GM alfalfa. The letter to Vilsack was essentially an intervention, Benbrook said.

“With the encouragement of certain GMO critics, Huber used the pending USDA decision on Roundup Ready alfalfa as an opportunity to raise the alarm over a yet unidentified… organism that could pose substantial new harm,” he said.

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“He didn’t have the data lined up. And we’re September 2013 and he still hasn’t published. Clearly, there was a little bit of premature warning in that letter.”

Benbrook said Huber’s allegation of a mysterious new pathogen may have gone too far, but the science community shouldn’t disregard his glyphosate research.

“Huber had a long and distinguished career. He was one of the first well-trained scientists to really focus on the impact of agricultural production systems on soil microbial communities,” he said, adding that the overuse of glyphosate has likely caused “the emergence of literally millions of strains of new bacteria, soil micro-organisms and viruses…. It is also inevitable that some small percent will not be benign.”

In response to Huber’s letter, a team of USDA and university experts conducted a review of glyphosate. They published a paper, Glyphosate Effects on Plant Mineral Nutrition, Crop Rhizosphere Microbiota and Plant Disease in Glyphosate Resistant Crops, last fall in the Journal of Agricultural and Food Chemistry.

Stephen Duke, lead author of the lengthy and complex paper, said the team of scientists not only reviewed the scientific literature but also spoke to growers and industry representatives to assess glyphosate.

“I was asked to evaluate the claims of Huber. He has three main claims,” said Duke, research leader with the USDA Natural Products Utilization Research unit in Mississippi.

“One is that mineral nutrition in Roundup Ready crops is not right. Two, that these crops are more susceptible to certain diseases. Three, there is a disease in the crops that’s a new disease, (which) is causing problems.”

The scientists did not examine Huber’s claim regarding a novel pathogen because of a lack of evidence.

“There isn’t one published paper in a refereed journal with any data on any of these claims,” Duke said. “These are claims he’s made without publishing any data.”

Duke and his colleagues concluded that concerns regarding plant disease and mineral nutrition in herbicide tolerant crops “are based on publications from a limited number of researchers” and the significance of those studies is questionable.

“Reports of significant adverse effects of glyphosate on mineral nutrition and diseases of GR (glyphosate resistant) crops are perplexing in light of the considerable body of literature and yield data that contradict such claims,” the authors said.

“Nevertheless, there might be effects of glyphosate in GR crops on mineral nutrition and/or disease under particular but uncommon conditions.”

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In light of that conclusion, Duke is now conducting a multi-site study in which growers apply high levels of glyphosate to Roundup Ready corn and soybeans to evaluate the herbicide impact on plant disease.

Mainstream agricultural scientists may reject Huber’s arguments, but his ideas regarding glyphosate aren’t going away, said Fred Kirschenmann, distinguished fellow with the Leopold Centre for Sustainable Agriculture at the University of Iowa.

Using a single tactic to control weeds isn’t sustainable, and growers are starting to see the consequences to soil and plant health, said Kirschenmann, who farms in North Dakota.

“It’s not that glyphosate is the problem. It’s that glyphosate is part of a pest management strategy that is the problem.”

Benbrook agreed there is a need for more studies on herbicide tolerant systems and how they affect plant health. Yet, at this point, the macro-evidence suggests that glyphosate isn’t seriously compromising soil or plant health, he added.

“The fact that 98 percent of farmers are still planting Roundup Ready soybeans, they wouldn’t be doing it if they felt they were really losing a lot of yield.”

In the end, the rapid development and spread of resistant weeds and farmer response to that conundrum will play a much larger role in glyphosate’s future than fears about plant disease or soil-based pathogens, Benbrook said.

“If people want to save glyphosate as an effective herbicide, it better be down below 50 percent (of current usage),” he said.

“I hope farmers come to their senses and realize if they want to save this technology, they’re probably going to have to do it themselves.”

Other stories in this Special Report:

UN report released March 20, 2015UN body declares glyphosate probable human carcinogen

Contact robert.arnason@producer.com

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