Roundup is a benign herbicide that makes life easier for farmers
Roundup causes soil and plant problems that impact yield
GM Roundup Ready crops are marketed on the basis that Roundup is a safe herbicide that simplifies weed control and makes the farmer’s life easier. But recent studies show that Roundup and glyphosate can accumulate in plants, have negative effects on soil organisms, and harm the growth and health even of soy plants that are genetically engineered to tolerate it. These effects may be partly responsible for yield decline and disease outbreaks found in GM Roundup Ready soy and maize.
5.7.1. Glyphosate causes or exacerbates plant diseases
“When you spray glyphosate on a plant, it’s like giving it AIDS.”
– Michael McNeill, agronomist and farm consultant97
Manufacturers claim that glyphosate kills plants by inhibiting an enzyme necessary for plant growth. But research shows that glyphosate has another way of killing plants: it makes the plant more susceptible to disease, potentially leading to the plant’s death from the disease. Spraying glyphosate on a plant is, as US agronomist Michael McNeill said, “like giving it AIDS”.
One possible mechanism for this process is offered in a study on GM RR soybeans. The study found that once glyphosate is applied to the plant, it accumulates in the plant tissues and then is released into soil through the roots. There, it stimulates the growth of certain fungi, notably Fusarium, a fungus that causes wilt disease and sudden death syndrome in soy plants.98 Other studies confirm the link between glyphosate applications and increased infection with Fusarium.99,100,101,102,103
Interestingly, one study found that Fusarium colonisation of roots was greater in GM RR soy compared with non-GM soy even when glyphosate is not applied. The researchers suggested that this was due to an unintended change in the GM crop brought about by the genetic engineering process.98
Fusarium is of especial concern because it does not only affect plants. It produces toxins that can enter the food chain and harm humans108 and livestock. In pigs, Fusarium-contaminated feed impairs reproduction105 and increases stillbirths.106
Glyphosate has also been shown to increase the incidence and severity of other fungal diseases in plants, including take-all in wheat and Corynespora root rot in soy.107,108
In an attempt to combat soil-borne diseases such as Fusarium, Monsanto markets its new Roundup Ready 2 Yield soy seed with a proprietary fungicide/insecticide coating.109 In other words, Monsanto has created a problem (fungal infection) by genetically modifying the soy seeds and is then profiting from a techno-fix “solution” to that problem. Such chemical treadmills are profitable for seed and chemical companies, but hurt farmers, consumers, and the environment.
5.7.2 Glyphosate makes nutrients unavailable to plants
Glyphosate binds vital nutrients such as iron, manganese, zinc, and boron in the soil, preventing plants from taking them up.110 So GM soy plants treated with glyphosate have lower levels of essential nutrients and reduced growth, compared with GM and non-GM soy controls not treated with glyphosate.111 Lower nutrient uptake may partly account for the increased susceptibility of GM soy to disease, as well as its lower yield. It could also have implications for humans and animals that eat the crop, as it is less nutritious.
5.7.3 Glyphosate impairs nitrogen fixation
The yield decline in GM RR soy may be partly due to glyphosate’s negative impact on nitrogen fixation, a process that is vital to plant growth and depends on the beneficial relationship between the soy plants and nitrogen-fixing bacteria. In young RR soy plants, glyphosate has been found to delay nitrogen fixation and reduce the growth of roots and sprouts, resulting in yield decline. In drought conditions, yield can be reduced by up to 25%.112
The mechanism may be explained by another study, which found that glyphosate enters root nodules and negatively affects beneficial soil bacteria that are essential for the nitrogen fixation process. It inhibits root development, reducing root nodule biomass by up to 28%. It also reduces by up to 10% an oxygen-carrying protein, leghaemoglobin, which helps bind nitrogen in soybean roots.113
To counter such problems, seed and agrochemical companies have begun to market a “techno-fix” in the form of nitrogen-fixing bacterial inoculants, which are either applied to soy seed before sale or to the soil after sowing. The companies claim that this will increase yield potential.114 However, a soybean inoculant evaluation trial conducted in Iowa concluded, “none of the inoculants resulted in a significant yield increase over the non-inoculated plots”.115 Inevitably, the cost of such treatments, even when they do not work, are borne by farmers.
Roundup and other glyphosate herbicides are not benign but have negative effects on soil and crops, some of which impact plant health and yield. Glyphosate’s link with Fusarium infection is especially serious as Fusarium can harm humans and livestock.