Title: Australian weed resistances a warning for New Zealand
[Stuff.co.nz 16 Dec 2011 by Tim Cronshaw] -- The resistance of weeds in Australia to the most widely used herbicide in agriculture has scientists worried it is only a matter of time before New Zealand has to deal with the same problem. Australia has six weeds resistant to glyphosate, often sold under the trade name Round-Up, and their growth over thousands of hectares of uneconomic farmland is forcing farmers to walk off some properties. Scientists have found 65 per cent of the 368 resistant weed populations have evolved in conditions similar to New Zealand. Only 35 per cent of them occurred in cropping and the rest were in roadsides, along fence lines or in horticultural tree crops. AgResearch senior scientist Trevor James said farmers needed to take the resistance problem seriously as it would be found in New Zealand "sooner or later" because there was already some resistance to other chemicals.
"It's a huge threat in Australia, next to salination in their cropping . We thought it was from the different cropping practices that created the problem, but 65 per cent of the resistant weeds are caused by practices duplicated in New Zealand on our fence lines and roadsides."
He said the resistance developed after repeated applications of the same chemical, and every so often a weed would have a "spontaneous mutation". If the mutation was allowed to grow to a decent-sized population, a large problem would be created.
Farmers are being advised to watch for small patches of green or plant survivors in sprayed areas and along roadsides and fence lines where glyphosate is regularly used.
James said the way to prevent the problem was to rotate chemicals and use different modes of operation.
New Zealand farmers had been told for the past 15 years to rotate their chemicals and some were better than others at following this advice.
Those less diligent treated it as tomorrow's problem, he said.
"[Glyphosate] is a silver bullet with a few side-effects. We have to learn to shoot the silver bullet effectively."
New Zealand had dealt with weed resistance to different chemicals since the 1980s, but glyphosate resistance was a larger threat because it would affect a wider range of people, he said.
Of the resistant grasses and broadleaf weeds in Australia, only one is not found in New Zealand.
Fleabane is one of the more common weeds and causes concern because it has a wind-borne seed and could spread easily.