Roundup

Weedkiller May Encourage Blight 

ANDY COGHLAN / New Scientist 14aug03

A widely used herbicide encourages the growth of toxic fungi that devastate wheat fields, laboratory studies by scientists working for the Canadian government suggest.

If field studies confirm that the herbicide, glyphosate, increases the risk of fungal infections - which are already a huge problem - farmers might be advised to use it less.

That could be a major blow for backers of genetically modified wheat in Canada, because the first GM variety up for approval in Canada is modified to be glyphosate-resistant. If it gets the go-ahead, there is likely to be an overall increase in glyphosate use.

The potential problem was spotted a few years ago by Myriam Fernandez of the Semiarid Prairie Agricultural Research Centre run by Agriculture and Agri-Food Canada in Swift Current, Saskatchewan. She noticed that in some fields where glyphosate had been applied the previous year, wheat appeared to be worse affected by fusarium head blight - a devastating fungal disease that damages grain and turns it pink.

Deadly toxins

In Europe alone, fusarium head blight destroys a fifth of wheat harvests. The fungi that cause the disease also produce toxins that can kill humans and animals.

In a follow-up study, Fernandez measured levels of the blight in wheat fields. "We found higher levels of blight within each tillage category when glyphosate had been used in the previous year," says her colleague Keith Hanson.

And his lab study 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.

But the investigators warn against jumping to conclusions. "We're deferring judgement until we have all the data," says Hanson. His team is now planning field and greenhouse trials.

Dead plant matter

Hanson stresses that the real issue is whether the fungi leave more spores in the soil. It is also possible that the effect is simply due to herbicides leaving more dead plant matter in the soil for fungi to grow on and is not directly caused by glyphosate. His field studies should provide answers next spring, he says.

Monsanto, the company based in St Louis, Missouri, that sells glyphosate as Roundup, as well as a number of "Roundup Ready" crops modified to be resistant to it, claims that glyphosate is already widely used without causing any apparent problems with fungi. Monsanto applied to the Canadian government in December 2002 for approval of its Roundup Ready GM wheat. It says it will be keeping a close watch on Hanson's research.

The team's initial 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.

Ironically, Syngenta, another biotech giant, based in Basle, Switzerland, has been developing and testing both GM and conventional wheat strains that are resistant to the fusarium head fungi. "The results have been promising," says a Syngenta spokesman.

source: http://www.newscientist.com/news/print.jsp?id=ns99994051 14aug03