RESEARCHERS say 23 weed species are now at high risk of developing glyphosate resistance, including several important grasses and damaging environmental weeds like fireweed and parthenium weed.
Australian Glyphosate Sustainability Working Group executive officer Andrew Storrie said most of the weeds tested were found across Australia and one in 10 weed species had a high risk of glyphosate resistance.
Where a species is at high risk of developing glyphosate resistance, it is vital not to rely on a single herbicide.
"While resistance to glyphosate in cropping has been making headlines around the world, this study suggests it could become a problem in any Australian weed management situation," Mr Storrie said.
Two hundred weed species were analysed to determine their innate likelihood to evolve and change in response to continued selection by herbicides in projects funded under the recently completed Department of Agriculture, Fisheries and Forestry (DAFF) National Weeds and Productivity Research Program managed by Rural Industries Research & Development Corporation (RIRDC), involving Department of Agriculture, Fisheries & Forestry Queensland and a number of other organisations.
Queensland Department of Agriculture, Fisheries and Forestry project member, David Thornby, said weed managers had a range of weed management tactics available to them for each species.
"Where a species is at high risk of developing glyphosate resistance, it is vital not to rely on a single herbicide," Dr Thornby said.
"Most weed managers have multiple problems competing for scarce resources - labour, time, money and attention - and risk assessments can be used by managers to help them decide how to organise their resources.
"From a resistance management perspective, it makes sense to devote more time to planning and monitoring, and increasing the range of management options, to species that appear to be at the highest risk of evolving herbicide resistance."
Dr Thornby said it was important to remember there is no relationship between resistance risk and weediness, invasiveness, or ease of control.
"What this study shows is that we need to be thinking about how we use herbicides in every situation, both agricultural and non-agricultural weed control," he said.
The top five highest risk weeds were:
- needle burr
- sweet summer grass
- Vulpia species
- flaxleaf fleabane
- liverseed grass.
The latter two species have already evolved resistance to glyphosate in Australia.
"Luckily almost half of all species assessed are at low risk of resistance, and the remainder at moderate risk," Dr Thornby said.
"Despite being at low risk of resistance, some low-scoring species are nevertheless important and highly prevalent weeds, both to cropping (e.g. nutgrass, bladder ketmia) and non-cropping areas (e.g. salvinia, alligator weed)."
Mr Storrie said market research as part of the project found many land managers were ill-prepared to deal with the loss of herbicides through resistance.
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