Herbicide promotes toxic fungi

Published: Tuesday 30 September 2003

glyphosate, the world's most widely used herbicide, encourages the growth of toxic fungi that devastate wheat fields. This is the alarming finding of a study conducted by scientists working for the Canadian government. The conclusion could prove to be a major blow for backers of genetically modified (gm) wheat, especially in Canada -- the first gm wheat variety of the country is modified to be glyphosate-resistant. If the crop is allowed to be commercially cultivated, there is likely to be a huge increase in the use of glyphosate.

The problem was spotted during a five-year study conducted by researchers of the Semiarid Prairie Agricultural Research Centre run by Agriculture and Agri-Food Canada. They noticed that in some fields where glyphosate had been applied just before planting, wheat appeared to be worse affected by fusarium head blight -- a devastating fungal disease that damages grains and turns them pink. In Europe alone, fusarium head blight destroys one-fifth of the wheat harvest. The fungi that cause the disease also produce toxins that can kill humans and animals.

"We found higher levels of blight within each tillage when glyphosate had been used," says Keith Hanson, one of the researchers. A laboratory test showed that Fusarium graminearum and F avenaceum , the fungi that cause head blight, grow faster when glyphosate-based weedkillers are added to the nutrient medium required for the fungi to grow.

But the investigators warn against jumping to conclusions. Hanson says it is also possible that the effect is due to herbicides leaving more dead plant matter in the soil for fungi to grow on.

The team's findings are likely to be seized upon by anti-gm activists. But switching to other herbicides could be bad news for the environment -- glyphosate is one of the least harmful herbicides, as it quickly breaks down in the soil. Some pro-gm technology experts concur that the new research is not so much a blow as every change is likely to have some unpredicted effects.

Monsanto, the company that sells glyphosate under the brand name Roundup, denies the results. In December 2002, it requested the Canadian government to approve its Roundup Ready gm wheat. Ironically, Syngenta, another biotech giant, has been developing and testing both gm and conventional wheat strains that are resistant to the fusarium head blight.

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