Data shows resistance is holding firm

12 Feb, 2018 04:00 AM
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Australia Herbicide Resistance Initiative senior research officer Mechelle Owen.
Australia Herbicide Resistance Initiative senior research officer Mechelle Owen.

LATEST research about the herbicide resistance status of WA’s major cropping weeds will be revealed at the Grains Research and Development Corporation’s (GRDC) Grains Research Update at Crown Perth on Monday, February 26 and Tuesday, February 27.

Australia Herbicide Resistance Initiative (AHRI) senior research officer Mechelle Owen will unveil results 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 had 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,” Ms Owen said.

The AHRI survey, carried out with GRDC investment, involved visits to 507 WA cropping paddocks and the 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 70pc of the populations sprayed had resistance to the ALS herbicide mixture imazamox+imazapyr.

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

“Screening with atrazine indicated 17pc 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).”

While testing annual ryegrass, Ms Owen said of the 338 populations treated with diclofop (ACCase inhibitor), 96pc of populations contained resistant plants while 83pc also had resistance to sethoxydim.

“But the knockdown herbicides glyphosate and paraquat (photosystem I inhibitor) provided good control of most annual ryegrass populations,” Ms Owen 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 doing a great job at keeping weed numbers low,” Ms Owen said.

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

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

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

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