[FarmWeekly 22 Sept 2011 by BOBBIE HINKLEY] -- DESPITE early findings a stronger concentration of glyphosate doesn't mean better weed kill. Former WA No-Tillage Farmers Association (WANTFA) agronomist and Australian Herbicide Resistance Initiative (AHRI) PhD student Mike Ashworth said a high water level was in fact the key to an effective knockdown. "This trial basically looks at the effect of water rate, herbicide rate and timing in Roundup Ready (RR) canola," he said. "A lot of past research has shown 30 litres of water a hectare, or a lowered water rate is really effective. "But what we're finding here at this trial is that water rates around the 80 litres a hectare to 100L/ha allows growers to get really good weed kill coverage."
He said in the past there had been a number of reasons why lowered water rates were considered the most effective.
The most common idea was the theory of high concentration.
"What we find now is growers need to make sure they keep their water rates robust in RR crops because they can't afford to under-dose any plants and begin to select for specific plants in the paddock," he said.
"Farmers also need to keep their herbicide rates up because it's a cheap to do and we don't want growers to select for resistance."
Mr Ashworth's PhD studies benchmarked levels of glyphosate efficacy on weeds.
He said his work looked at the potential risk of glyphosate resistance development in genetically modified (GM) canola with a real focus on wild radish resistance.
"I've just finished a Statewide survey where I travelled 7000 kilometres and surveyed 22,500 hectares of GM crops," he said.
"I found significant survival of wild radish and ryegrass which indicates a potential issue with spray application.
"My initial thoughts were that maybe growers throughout the Wheatbelt are using too low a water rate for the glyphosate to get through the crop to the ground weeds at spray time."
Mr Ashworth's survey also highlighted the inherent tolerance to glyphosate in wild radish species.
He said a late germination of ryegrass and wild radish indicated there was a huge need for integrated weed management and harvest weed seed management precautions.
"Glyphosate is our most important herbicide and while growers are applying it at a higher concentration they're actually selecting for glyphosate resistance in a way," Mr Ashworth said.
He said glyphosate was known for its wide use in knockdown weed control prior to no-till seeding.
Glyphosate had a long history of use and was now being relied on more than ever.
"Growers are using it to control summer weeds to conserve soil moisture and now more than ever they're also using it for the post-emergent control of weeds in RR canola," he said.
"Like all herbicides, persistent glyphosate use on highly diverse weed species can lead to resistance."
Mr Ashworth inspected weed control early this growing season in as many RR canola paddocks throughout the State as possible.
While surveying the paddocks he rated the level of weed control and collected suspect survivor plants of a second glyphosate spraying for further research at the University of Western Australia (UWA).
Through his PhD studies Mr Ashworth has now started some experiments to study the low-dose evolution of glyphosate resistance in wild radish.
AHRI has also just started a wild radish flowering date study to find out if wild radish could potentially evade harvest weed seed management in the near future.
