Glyphosate Hazards to Crops, Soils, Animals, and Consumers
In less than an hour, Don Huber, professor emeritus at Purdue University and USDA senior scientist (see Box) delivered to the UK Houses of Parliament a damning indictment of glyphosate agriculture as a most serious threat to the environment, livestock, and human health .
Don Huber, Emeritus Professor at Purdue University and senior scientist on USDA’s National Plant Disease Recovery System, has been a plant physiologist and pathologist for over 40 years. His academic career began with 8 years as a cereal pathologist at the University of Idaho, and the next 35 years at Purdue University where he specialised in soil-borne disease control, physiology of disease, and microbial ecology. For the past 20 years, he has conducted extensive research into the effects of glyphosate on crops, in response to the increase in crop diseases on glyphosate-applied fields.
Since his letter to the US Secretary of State Tom Vilsak was leaked in February 2011, there has been a great deal of controversy over what Huber described as a pathogen “new to science” and abundant in glyphosate-tolerant GM crops (see  Emergency! Pathogen New to Science Found in Roundup Ready GM Crops?, SiS 50). As he concluded in the letter: “We are now seeing an unprecedented trend of increasing plant and animal diseases and disorders. This pathogen may be instrumental to understanding and solving this problem”.
His talk linked glyphosate to reduced nutrient availability in plants, increasing plant diseases, the emergence of a new pathogen, animal illness and possible effects on human health (see [3, 4] Glyphosate Tolerant Crops Bring Death and Disease, Scientists Reveal Glyphosate Poisons Crops and Soil, SiS 47).
Pathogen new to science
The conversion of US agriculture to monochemical herbicide practice has resulted in the extensive use of glyphosate herbicides. Coincidentally, farmers have been witnessing deterioration in the health of corn, soybean, wheat and other crops, and epidemics of diseases in small grain crops. All are associated with the extensive use of glyphosate, which has increased further since the introduction of glyphosate-tolerant, Roundup Ready (RR) crops.
Glyphosate immobilises nutrients required to maintain plant health and resistance to disease. This weakening of the plants defence could explain the infestation of GM crops with the new pathogen, which has now been observed in horse, sheep, pigs, cows, chicken, multiple animal tissues including reproductive parts (semen, amniotic fluid), manure, soil, eggs, milk, as well as the common fungal pathogen that is currently infesting RR crops, Fusarium solani fsp glycines mycelium. All are coming into contact with glyphosate either through direct exposure or consumption through animal feed. It is also highly abundant in crops suffering from plant Goss’ wilt and sudden death syndrome.
The pathogen can be cultured in the lab, and has been isolated from livestock foetal tissue, replicated in the lab and re-introduced back into the animals. It appears to be very common and may well be interacting with the effects of glyphosate on both plants and animals, exacerbating disease and causing reproductive failure in livestock (see below). Although great expectations have been placed on Huber to publish his findings, he insists that before this can be done, further resources are necessary to be able to characterise the ‘entity’ and identify what type of species it is, including sequencing of its genome. This is a slow process and once complete, it is his intention to publish the work in a peer-reviewed journal.
Understanding glyphosate’s mode of action
Recognising glyphosate’s mechanism of action is the key to understanding how it may exert detrimental effects on the health of crops, animals, and the environment alike. Glyphosate is a broad-spectrum herbicide that interacts with a range of physiological processes in the plant and its environment. Although it is most commonly recognised to work through inhibition of the plant enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) involved in the production of aromatic amino acids in the shikimate pathway, it was actually first patented as a strong metal-chelator that binds to metals including manganese, magnesium, iron, nickel, zinc and calcium, many of which are important micronutrients acting as co-factors for plant enzymes in different physiological processes including the plants’ defence system. Indeed, it is actually through chelation of manganese that the EPSPS enzyme is inhibited.
Rendering plants more susceptible to disease through glyphosate’s pathogenic activity is actually the way it exerts its herbicidal activity. This is done not just through immobilising nutrients in the plant but also impacting the agricultural system as a whole. Consistently, if glyphosate does not reach the root of a plant or the plant is grown in a sterile soil, the plant is not killed.
Once in the soil, glyphosate is later immobilised through the chelation of cations, and is therefore very stable and not easily degraded. However, phosphorus (including phosphorus fertilisers) can desorb the herbicide, making it active once again in the soil.