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Renewed debate about GM crops with herbicide resistance

Is glyphosate dangerous? Anti-herbicide campaign on shaky ground

Don Huber, a retired American professor of plant pathology, is giving a lecture tour in Germany in October 2011. He warns of the consequences of using the broad-spectrum herbicide glyphosate, also known under its brand name Roundup, which is used in conjunction with the cultivation of herbicide-tolerant GM crops. According to Huber, the herbicide leads to malnourished plants, to an increase in plant diseases and to significant declines in yield – claims that his former colleagues at Purdue University (USA) vehemently deny. In Germany, Huber’s claims have fallen on fertile soil among environmental associations and Die Grünen (Germany’s Green Party), which for some time have been calling for the glyphosate authorisation to be suspended.

Don Huber

Don Huber, Professor Emeritus at Purdue University, warns of possible dangers associated with glyphosate.

Agricultural company Monsanto filed a patent for Glyphosate as a broad-spectrum weed-killer in the 1970s. It is used in agriculture, but also in private gardens and to control weeds along roads and railway lines. Since 1996, when the first GM crops with glyphosate tolerance were planted, glyphosate has been used more widely. Around a million tonnes of it were sold worldwide in 2010. For a long time, Monsanto owned the patent for the herbicide, but it expired in most countries over 10 years ago. A large proportion of the glyphosate sold today is produced in Asia.

In Don Huber’s scientific investigations, glyphosate-tolerant GM plants were found to be more susceptible to a range of plant diseases. The reason given is that glyphosate binds important nutrients like manganese and zinc in the soil and in plant cells, which means they are not then available to the crop plants. This, it is claimed, weakens the plants’ ability to fight off pathogens.

In January 2011, Huber wrote a letter to US Secretary of Agriculture Tom Vilsack informing him that he and his colleagues had discovered a new, electron microscopic pathogen that was attacking glyphosate-tolerant GM plants. According to Huber, glyphosate promotes the soil pathogen and could lead to diseases in plants and mammals. The researcher is sounding the alarm, saying that the use of Roundup should be viewed as a calamity. The pathogen was also found in animals that had been fed on these plants and had experienced spontaneous abortions or were infertile. The letter found its way into the press in summer 2011.

In an open letter, the President of the American Phytopathological Society (APS) made it clear that in this case Huber was not representing APS, and criticised the fact that the findings relating to the new pathogen had not been published in a scientific journal. There was no verifiable evidence available to support the claim.

Scientists at Purdue University, where Huber lectured until he retired, also refuted his theories. Although they shared his general observation that glyphosate can make plants more susceptible to individual pathogens, they said that this fact had been known for some time and was also true of other herbicides. Glyphosate has, they say, been used on a large scale for more than 30 years and there are no indications of any general increase in plant diseases or associated yield losses as claimed by Huber. In cases where there had been an increase in plant diseases, these could have been caused by something else. For instance, the increase in soil-friendly farming methods with little or no ploughing could be a factor. Pathogenic bacteria and fungi can survive better in plant remains that are left on the surface of the field instead of being ploughed in. The scientists also point out that a number of new high-yield varieties have come onto the market in quick succession in recent years and they could be less resistant to plant diseases. In any case, claims that glyphosate plays an important role in plant health are, they say, largely unfounded. When deciding whether or not to grow glyphosate-tolerant varieties, farmers should, they say, be governed by the facts and not by sensation-seeking claims.

Huber’s lectures join the debate about the safety of glyphosate that has been raging for some time in Germany among NGOs and political parties. For instance, Bündnis 90/Die Grünen and various environmental organisations are calling for an immediate suspension of the authorisation for herbicides containing glyphosate. They cite findings from a study by Argentinian embryologist Andre Carrasco published in 2010. Carrasco injected glyphosate into frog embryos, which caused the frogs to develop serious deformities. He saw this as proof that glyphosate can also disrupt human embryo development and as evidence that it was responsible for deformities among children in soya-growing areas in Argentina. Carrasco’s experiments and conclusions have, however, been disputed by other scientists. Above all, they doubt whether the high concentrations of glyphosate used in the tests are ever achieved in reality. The German Federal Office of Consumer Protection and Food Safety (BVL), which is responsible for authorising plant protection products in Germany, wrote in October 2010 that Carrasco’s study findings were not relevant for the current risk assessment of glyphosate for humans because of methodological weaknesses and a lack of data.

In response to a minor parliamentary question submitted by the Bündnis 90/Die Grünen parliamentary group at the end of August 2011 on the current risk assessment of glyphosate, the German government said that the data currently available did not justify a suspension or restriction of the authorisation for herbicides containing glyphosate. Neither was there any need to adjust the limits for glyphosate residues. The government cites numerous animal experiments that have provided no indication of genotoxic or carcinogenic risks associated with glyphosate. Germany’s Federal Institute for Risk Assessment (BfR) expressed a similar view in a statement issued in July 2011.

A recent study by the Institute of Agribusiness in Giessen shows that glyphosate is used on a third of farmland in Germany – not as a complementary herbicide for herbicide-tolerant GM crops, but as a standard part of a conservation tillage approach. According to the study, suspending the authorisation of glyphosate would lead to a significant increase in tillage and greater use of other herbicides.

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