GM Free Cymru

Scientists Reveal Glyphosate Poisons Crops and Soil

GM Meltdown Continues

Scientists go public on devastating ecological impacts of Roundup Ready cropping systems while USDA keeps mum

Dr. Mae-Wan Ho

ISIS Report 19/05/10

Dire consequences from the most widely used herbicide in the world

Glyphosate-tolerant (GT) crops have spread rapidly around the world since they were introduced in the US in 1996, and are now planted on 85 percent of the global area growing genetically modified (GM) crops [1]. Concomitantly, glyphosate (commercial formulation Roundup), promoted as safe for health and the environment, became the most widely used herbicide in the world.

But ecological and health impacts of the GT cropping system soon came to light, and have been worsening relentlessly over the years while regulators turn a blind eye (see [2, 3] Roundup Ready Sudden Death, Superweeds, Allergens..., SiS 28; Ban Glyphosate Herbicides Now, SiS 43).

Glyphosate binds with and inactivates EPSPS, the critical enzyme in the shikimate pathway required for the synthesis of aromatic plant metabolites including essential amino acids phenylalanine, tryptophan and tyrosine, as well as downstream products such as plant growth promoter, indoylacetic acid and plant defence compounds, phytoalexins [4]. But glyphosate has multiple adverse effects that act synergistically on crop health and productivity that extends well beyond the plant into the soil ecosystem and the wider environment.

The GT trait depends on incorporating an EPSPS from the soil bacterium Agrobacterium tumefaciens that is insensitive to glyphosate, hence glyphosate is taken up by GT plants and translocated to the growing parts of roots and shoots, and even exuded into the rhizosphere (soil surrounding the roots) so it can affect the soil community of microorganisms and also subsequent crops planted in the soil.

Two senior scientists in the US who have been investigating the ecological impacts of glyphosate and the Roundup Ready cropping system for decades are warning of “dire consequences for agriculture such as rendering soils infertile, crops non-productive, and plants less nutritious.”

Glyphosate the single most important factor predisposing plants to diseases and toxins Don Huber, recently retired from Purdue University, and co-author G.S. Johal, at Purdue’s Dept of Botany and Plant Pathology, stated in a paper published in the October 2009 issue of European Journal of Agronomy that the widespread use of glyphosate in the US can “significantly increase the severity of various plants diseases, impair plant defense to pathogens and diseases, and immobilize soil and plant nutrients rendering them unavailable for plant use.”

Further, glyphosate stimulates the growth of fungi and enhances the virulence of pathogens such as Fusarium, and “can have serious consequences for sustainable production of a wide range of susceptible crops.” They warn that “Ignoring potential non-target detrimental side effects of any chemical, especially used as heavily as glyphosate, may have dire consequences for agriculture such as rendering soils infertile, crops non-productive, and plants less nutritious.”

In an interview [5] with the Organic & Non-GMO Report, Huber said he has been researching glyphosate for 20 years, and began noticing problems when he saw a consistent increase in “take-all”, a fungal disease of wheat, when glyphosate had been applied in a previous year to control weeds. He found glyphosate reduced manganese in plants, which is essential to many plant defence reactions against disease and environmental stress. Glyphosate can immobilize plant nutrients such as manganese, copper, potassium iron, magnesium, calcium, and zinc, so they are no longer nutritionally functional. Basically, glyphosate completely weakens the plant, making it susceptible to soil-borne fungal pathogens. “That is one reason why we see an increase in plant diseases,” he said.

There has been a general increase in the number of plant diseases in the past 15 to 18 years. Four primary soil fungi, Fusarium, Phythium, Rhizoccccctonia, and Phytophthora, have become more active with the use of glyphosate; and concomitantly, diseases caused by these fungi have increased, such as head scab in corn, or root rot in soybeans, crown rot in sugar beets. Fusarium head blight, which affects cereal crops, is a disease that produces a mycotoxin that could enter the food chain.

There are more than 40 diseases reported with the use of glyphosate, and the number keeps growing as people recognize the association, Huber said.

When asked if glyphosate is “environmentally benign” as claimed by proponents, he answered “Absolutely not. That’s an outright mistaken notion. Glyphosate is the single most important agronomic factor predisposing some plants to both disease and toxins. These toxins can produce a serious impact on the health of animals and humans.

“Toxins produced can infect the roots and head of the plant and be transferred to the rest of the plant.” Huber explained. “The toxin levels in straw can be high enough to make cattle and pigs infertile.”

One way in which glyphosate can affect human health is that “micronutrients such as manganese, copper, potassium, iron, magnesium, calcium, and zinc are essential to humans. All of them can be reduced in availability by glyphosate; so glyphosate treated GT plants as well as other plants exposed to glyphosate have less mineral nutrients. “We are seeing a reduction in nutrient quality [in our food].”

“The [Roundup Ready] gene will reduce micronutrient efficiency up to 50 percent for zinc and manganese…This could also account for the yield drag [reported for GT soybeans].”

“Unfortunately, most researchers are forbidden to do work in the area. They don’t have access to isogenic lines [conventional and Roundup Ready plant lines that are otherwise genetically identical], the materials are denied to researchers.”

Huber and Johal recommend using as little glyphosate as possible.

Unfortunately, reducing the dose of glyphosate will be insufficient for killing weeds, particularly as numerous weeds are becoming highly resistant to the herbicide (see [6] GM Crops Facing Meltdown in the USA, SiS 46)

Roundup Ready system alters the whole soil biology Robert Kremer is a microbiologist with the USDA-ARS (US Department of Agriculture- Agricultural Research Service) and an adjunct professor in the Division of Plant Sciences at the University of Missouri. He started in 1997 to investigate how the new Monsanto Roundup Ready system (Roundup herbicide and GT cropping) would change the level of nematodes in soybean. His research team began looking at the roots and saw microorganisms colonizing the roots, and suspected that glyphosate was having an impact. There was a root fungi problem that seemed to encourage sudden death syndrome.

In fact, the system is “altering the whole soil biology.” Kremer told The Organic & Non-GM Report [7]. “We are seeing differences in bacteria in plant roots and changes in nutrient availability. Many studies show that glyphosate can have toxic effects on [some] microorganisms and can stimulate [others] to germinate spores and colonize roots systems. Other researchers are showing that glyphosate can immobilize manganese, an essential plant micronutrient.”

Glyphosate is toxic to beneficial bacteria like rhiozbia, which fixes nitrogen, but increases the incidence of pathogens like Fusarium. “Some Roundup Ready varieties even without using glyphosate, tend to be more susceptible to Fusarium,” possibly an unintended effect of genetic modification.

If the soil is full of phosphate (as when livestock manure is used as a fertilizer), glyphosate could leach into ground water (and poison other wild-life and human beings).

“We saw the increase of these fungi in the Roundup Ready system, both soybeans and corn.” Kremer said.

The papers describing the work of his research team, published in the European Journal of Agronomy [8] received no publicity in the US. Kremer said [7]: “I was working with USDA-ARS to publish a news release about these studies. I’ve gone all the way to the administrators, but they are reluctant to put something out. Their thinking is that if farmers are using this (Roundup Ready) technology, USDA doesn’t want negative information being released about it. This is how it is. I think the news release is still sitting on someone’s desk.”

Kremer concluded [7]: “We’re looking at some methods that could be used to overcome negative effects if we continue to use Roundup Ready crops, such as supplementation of nutrients by foliar application,” but added, “I’m more interested in sustainable agriculture. More farmers are interested in using cover cropping to maintain soil quality and other organic amendments. But it’s a steep learning curve for them.”

References 1. Yamada T. Kremer RJ. De Carmargo e Castro and Wood BW. Glyphosate interactions with physiology, nutrition, and diseases of plants: threats to agricultural sustainability? Europ J Agronomy 2009 31, 111-3

2. Ho MW and Cummins J. Roundup Ready sudden death, superweeds, allergens…time to wipe GM crops off the globe. Science in Society 28, 26-27, 2005.

3. Ho MW. Ban glyphosate herbicides now. Science in Society 43, 34-35, 2009.

4. Johal GS and Huber DM. Glyphosate effects on diseases of plants. Eur J Agron 2009, 144-52.

5. “Scientist warns of dire consequences with widespread use of glyphosate”, The Organic & Non-GMO Report, May 2010,

6. Ho MW. GM crops facing meltdown in the USA. Science in Society 46 (in press).

7. “Scientist finding many negative impacts of Roundup Ready GM crops, USDA doesn’t want to publicize studies showing negative impact2, The Organic & Non-GMO Report, January 2010,

8. Kremer RJ and Means NE. Glyphosate and glyphosate-resistant crop interactions with rhizosphere microorganisms. European Journal of Agronomy 2009, 31, 153-61.