Survey shows herbicide resistance in WA stable

Mechelle Owen, Australia Herbicide Resistance Initiative (AHRI) Senior Research Officer. Image courtesy of GRDC

Latest results about the herbicide resistance status of Western Australia’s major cropping weeds will be revealed at the State’s upcoming premier grains research forum, the Grains Research and Development Corporation’s Grains Research Update, Perth on February 26 and 27 2018.

Australia Herbicide Resistance Initiative (AHRI) Senior Research Officer Mechelle Owen will unveil the results which were generated from testing a random collection of weed samples from across the grainbelt in 2015.

Ms Owen said preliminary data from the weed analysis suggested herbicide resistance in wild radish and annual ryegrass has not increased dramatically since 2010 for commonly used herbicides.

“Resistance against commonly used herbicides is still evident in key weed species, so growers need to use a range of integrated weed management tactics,” she said.

The AHRI survey, carried out with GRDC investment, involved visits to 507 WA cropping paddocks and collection of 734 seed samples, comprising seven weed species.

During the 2016 growing season, researchers treated wild radish populations with a range of herbicides.

“We found that, of the 65 populations sprayed with the ALS-inhibiting herbicide chlorsulfuron, 88 per cent of populations had resistant plants,” Ms Owen said.

“The results showed 70 per cent of the populations sprayed had resistance to the ALS herbicide mixture imazamox+imazapyr.

“For the synthetic auxin 2,4-D, there were 61 per cent of populations containing resistant plants and 65 per cent had plants resistant to diflufenican (PDS inhibitor).

“Screening with atrazine indicated 17 per cent of populations displaying resistance, although resistance levels haven’t changed significantly since the earlier surveys.

“It was positive that no populations exhibited resistance to the knockdown herbicide glyphosate (EPSPS inhibitor).”

Ms Owen said, for annual ryegrass, of the 338 populations treated with diclofop (ACCase inhibitor), 96 per cent of populations contained resistant plants and 83 per cent also had resistance to sethoxydim.

“But the knockdown herbicides glyphosate and paraquat (photosystem I inhibitor) provided good control of most annual ryegrass populations,” she said.

“No populations had resistance to paraquat, but some populations displayed resistance to glyphosate.”

Ms Owen said testing in 2017 found that no populations of brome or barley grass had resistance to fluazifop, clethodim, glyphosate or paraquat.

But she said some brome grass populations displayed resistance to the sulfonylurea (SU) herbicides sulfosulfuron and sulfometuron. Barley grass screening for the SU herbicides will be carried out during 2018.

“In spite of these latest herbicide resistance findings, our survey results since 1998 indicate growers are, in fact, doing a great job at keeping weed numbers low,” she said.

“We found there can be such variability that it pays for a grower to get to know the resistance profile for their own paddocks.

“For example, there are some paddocks where there are resistant plants present but 95 per cent control can be achieved with the right herbicide.”

Ms Owen said the evolution of herbicide resistant weed populations was now widespread right across southern Australia for the major cropping weeds, including annual ryegrass, wild radish and wild oats.

GRDC recognises the importance of managing this problem and invests about $1 million annually into AHRI, which is a research leader in understanding mechanisms of herbicide resistance and resistance management.

Further data from Ms Owen’s AHRI-led research will be presented at the GRDC Grains Research Update, to be held at Crown Perth on February 26 and 27 2018.

Source: GRDC

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