Resistance results confirm need for weed planning in Australia

Now is a good time for growers to scout crops for spray failures so planning can begin to stop weed seed set of annual ryegrass and other weed species this spring, according to the Australian Glyphosate Sustainability Working Group (AGSWG).

AGSWG executive officer Andrew Storrie said new annual ryegrass survey findings from South Australia provided further evidence of the need for significant changes to weed management to halt the development of glyphosate resistance.

Sixteen percent of randomly-collected annual ryegrass populations in the south-east of South Australia have tested resistant to glyphosate, the grains industry’s most important herbicide.

The random survey was conducted by the University of Adelaide and funded by the Grains Research and Development Corporation (GRDC).

Mr Storrie said high levels of resistance to glyphosate and other herbicide modes-of-action were also found in a targeted survey in WA conducted by the Stirlings to Coast Farmers grower group – in paddocks where herbicide resistance was suspected – in November 2011.

He said both the SA and WA surveys were in higher rainfall areas, but growers in lower rainfall areas were also at risk of weeds developing resistance to herbicides.

“From previous work, we knew there was some glyphosate resistance in the area surveyed in South Australia,” stated Chris Preston, project leader and Associate Professor at the University of Adelaide, “but this surprised all of us and has set the alarm bells ringing to bring in changes to weed management.”

Dr Preston recommends growers must use a range of tactics to ensure that the survivors of herbicide application don’t survive and set seed. Growers who are continuously cropping need to be rotating their knockdown herbicides, using the double-knockdown of glyphosate followed by paraquat where practical, and employing seed set control practices.These practices will help minimise the impact of glyphosate resistance.