A just confirmed case of annual ryegrass resistant to both glyphosate and paraquat is a warning to all farmers that rotating herbicide modes of action alone does not solve all your herbicide resistance problems, according to researchers.
The Australian Glyphosate Sustainability Working Group (AGSWG), supported by the Grains Research and Development Corporation (GRDC), said it was the first case of glyphosate plus paraquat resistance in any weed species in Western Australia and a world first for wine grapes.
The finding was made in a WA vineyard after Department of Agriculture and Food (DAFWA) senior researcher Sally Peltzer was alerted to the problem by the vineyard owner.
“It isn’t just vineyard managers who need to be having a serious look at how they use knockdown herbicides, as it raises concerns about broadacre management practices as well,” Dr Peltzer said.
While the problem first appeared to be a paraquat failure, treating samples with glyphosate showed the ryegrass was failing to respond to that knockdown herbicide as well.
AGSWG executive officer Andrew Storrie said the multiple herbicide resistance appeared to have been caused by 20 years of unplanned rotating of paraquat and glyphosate when treating the vine row strip.
“The area was treated two to three times per season and there was no follow-up to ensure any weed survivors were prevented from setting viable seed,” he said.
“Lack of follow-up is common practice across all spheres of weed control, from broadacre fallows to the treatment of fence lines, road verges and vine and tree crops.
“The only way to manage resistance is to kill the survivors of any herbicide application.
“This can be done with what we call a ‘double knock’ which can be another herbicide mode-of-action or mechanical means such as cultivation, hand-pulling or heavy sustained grazing.”
Mr Storrie said that land managers should monitor weed control to ensure weeds did not survive and reproduce following herbicide use.
“Another measure they can employ is to tank-mix full rates of two herbicide modes of action, so if one fails there is a robust rate of the second herbicide to kill the weeds,” he said.
“The good news about this population of weeds in the short term is that they are still susceptible to Group A grass-selective herbicides which have been used to prevent any further seed set.”
For more information on managing glyphosate resistance visit the AGSWG web site www.glyphosateresistance.org.au
For information on herbicide sustainability and harvest weed seed control practices, visit the WeedSmart information hub at www.weedsmart.com
Caption: Glyphosate and paraquat resistant annual ryegrass under vines. PHOTO: Andrew Storrie, Australian Glyphosate Sustainability Working Group.
Sally Peltzer, DAFWA
08 9892 8504, 0407 423 047
08 9842 3598, 0428 423 577
Natalie Lee, Cox Inall Communications
08 9864 2034, 0427 189 827
GRDC Project Code