Never say die

Farmers and agricultural scientists in Australia are having a tough time battling a weed that has suddenly developed resistance to a herbicide

Published: Saturday 31 August 1996

the alarm bells started ringing in September last year when a farmer in Ethuca, a small town on the banks of the river Murray in Northern Victoria, Australia, tried to clear his farm of an annual ryegrass, Lolium rigidum , which is a routine practice before the plantation of summer crops. But even after long and periodic applications of glyphosate, the most widely used herbicide in the world, the weed refused to die ( New Scientist , Vol 151, No 2037).

The seeds of the weed were subsequently sent to Jim Prattley of the Department of Agricultural Engineering of the Charles Strut University in Wagga Wagga in New South Wales. After a series of sophisticated tests, Prattley confirmed that this was indeed the first species of ryegrass resistant to glypho-sate. "Resistance to glyphosate was not at all expected... but it remains to be seen whether this is an isolated case or is widespread," he added.

However, Monsanto Inc, the us agrochemical giant which markets glyphosate under the trade name of RoundUp, is playing down Prattley's findings as RoundUp accounts for an estimated us $1.5 billion of the com-pany's annual sales of us $9 billion. Tests are already under way at Monsanto headquarters in St Louis, Missouri, us . Bill Blowes, technical director of Monsanto in Melbourne, Australia, claims that "We have had false alarms in the past."

He cites some varieties of weeds in New Zealand, which apparently, were found resistant to glyphosate some years back. But the problem in that case was that glyphosate could not penetrate the plants' outer cuticles. The herbicide was accordingly modified and produced immediate results. Prattley, however, says that there is clear indication of the presence of the herbicide inside the plant and the only way to explain its inefficacy is the fact that the weed has somehow, grown a genetic resistance to it.

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