GLYPHOSATE-RESISTANT ryegrass has been confirmed at four new Australian locations.
The new populations take the total number of populations to 44, with 24 of the cases in broadacre cropping. All are in annual ryegrass.
New NSW populations come from a broadacre chemical fallow, an irrigation channel and fenceline. The fourth new population comes from a South Australian vineyard.
There has been no increase in the number of glyphosate resistant populations in WA.
National Glyphosate Sustainability Working Group (GSWG) chairman Rick Llewellyn said that while the new populations demonstrated the risk of too much reliance on glyphosate, the low number of new populations in broadacre cropping suggested growers' preventative action was making a difference.
"It's now 10 years since the first case of resistance to this valuable herbicide was discovered and many people had predicted much higher resistance levels by now," Dr Llewellyn said.
"We believe we are now seeing the positive pay-off from preventative action taken by the many growers who recognised their glyphosate use history had placed them at high risk of resistance and they did something about it."
Research from the University of WA has shown the rare nature of glyphosate resistance meant practices such as the double-knock can greatly reduce the likelihood of resistance developing and be a profitable strategy.
The GSWG has produced a guide that lists methods to reduce the risk of developing glyphosate resistance.
"The important thing now is for growers who are entering into high-risk situations such as no-till or winter fallow to recognise the risks and how they can be reduced," Dr Llewellyn said.
"We're clearly seeing that glyphosate resistance is not inevitable."
Details of glyphosate-resistant populations in Australia are listed on the Australian Glyphosate Resistance Register, compiled by Chris Preston from the Grains Research and Development Corporation-supported Weeds CRC.
The register and information on how resistance can be managed is available from the GSWG website at www.weeds.crc.org.au/glyphosate.