Testing times for weed resistance
GroundCover™ Issue: 122 | 02 May 2016 | Author: Melissa Wililams
Despite growing evidence of escalating levels of glyphosate resistance in Western Australia, creative management will ensure the sustainability of this vital Group M herbicide.
That is the advice of Australian Herbicide Resistance Initiative (AHRI) director Professor Stephen Powles, who spoke at the inaugural GRDC-supported Crop Protection Forum in Perth in November 2015.
This forum was coordinated by AHRI and the Curtin University-based Centre for Crop and Disease Management to bring together leading weed and pesticide-resistance researchers.
Professor Powles told participants that glyphosate is still working well on the majority of WA farms, but stressed that growers and advisers need to diversify its use with other herbicide modes of action and non-herbicide weed-control tactics to preserve its effectiveness in the long term.
“As I keep emphasising, diversity is the key and when on a good thing, don’t stick to it,” he said.
Random surveys of WA grainbelt paddocks by AHRI researcher Mechelle Owen in 2010 found seven per cent of 362 annual ryegrass (Lolium rigidum) samples had glyphosate resistance. This was up from one per cent in 2003.
Further herbicide resistance surveys conducted by AHRI in 2010 and 2011 in 239 paddocks of Roundup Ready® canola across WA found 3.3 per cent of annual ryegrass samples were glyphosate-resistant.
In these surveys, there was no glyphosate resistance found in wild oats (Avena), brome grass (Bromus) or barley grass (Hordeum).
In 2013, as part of a glyphosate, paraquat (Group L) and 2,4-D (Group I) resistance project, Department of Agriculture and Food, WA (DAFWA) senior research officer Dr Sally Peltzer coordinated a targeted pre-harvest survey across WA’s cropping areas to raise awareness about the spread of glyphosate resistance in the state.
She found 40 per cent of 172 samples of annual ryegrass from more than 150 farm properties had some glyphosate resistance.
Of these, 32 per cent had weak (or developing) resistance, eight per cent had intermediate resistance to the lower glyphosate testing rate and 11 per cent had high-level resistance.
It should be noted that the DAFWA survey targeted growers who had weedy paddocks, compared with AHRI’s random sampling.
In 2013, AHRI researchers uncovered Australia’s – and the world’s – first cases of glyphosate-resistant wild radish (Raphanus raphanistrum L.) populations in WA’s northern grain-growing region.
Professor Powles said random surveys in South Australia and New South Wales also revealed an increasing incidence of glyphosate resistance – to levels as high as 16 per cent in annual ryegrass in south-east SA (2012) and one to two per cent on the NSW Slopes region (2013).
He said these findings are consistent with analyses of weed samples sent to Australian herbicide-resistance testing services at Charles Sturt University and Plant Science Consulting.
Professor Powles said across Australia most glyphosate resistance is found where the herbicide is used persistently.
However, he said the good news is that it is still highly effective where growers are diversifying their weed-control practices.
Best-practice integrated weed management tactics are outlined on the national grains industry’s WeedSmart campaign website.
Professor Powles said growers who find herbicide ‘survivors’, or weedy patches, on their farms this year can send samples for a resistance test.
He said if resistance is confirmed, growers should act immediately and not allow the resistant weeds to set seed.
Professor Stephen Powles,
08 6488 7834,
Useful resources:Integrated Weed Management Hub
Glyphosate resistance fact sheet
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GRDC Project Code UWA00146
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