Glyphosate resistance found in two weed species

GLYPHOSATE-resistant annual ryegrass populations have been confirmed at 87 sites across Australia, prompting a warning to growers.

University of Adelaide weed expert Chris Preston said glyphosate resistance was also recently found in two other weed species in Australia.

"Three populations of awnless barnyard grass and two populations of liverseed grass have been confirmed resistant to glyphosate in a summer cropping/fallow situation in northern NSW," Dr Preston said.

"Resistance in these summer grass weeds has major implications for the management of summer fallows and weed control in summer crops.

"It also demonstrates that weeds other than annual ryegrass can evolve resistance to glyphosate."

Dr Preston said 20 populations of glyphosate-resistant annual ryegrass had so far been confirmed at fence lines from Western Australia to NSW. Another 11 populations had been confirmed in other uncropped areas, such as irrigation channels and firebreaks.

"Fence lines offer fewer options for controlling glyphosate-resistant annual ryegrass," Dr Preston said.

"Tillage and competition are more difficult to employ, so herbicides will likely remain the main option."

He said glyphosate and glyphosate mixes did not provide effective control.

"Current research indicates paraquat mixed with amitrole or diuron provided better control of both resistant and susceptible annual ryegrass," he said.

"Growers should use robust rates of products on fence lines to ensure control."