These non-crop areas are a breeding ground for developing herbicide-resistant weeds, often spreading masses of seeds before farmers can control them.
University of Adelaide academic Peter Boutsalis said glyphosate and paraquat resistance was becoming a particular concern in cropping paddocks as seed spread into them from fence lines and other non-cultivated areas.
“This rise in paraquat resistance demonstrates that treating large weeds on fence lines with knockdown herbicides in spring is unsustainable,” Dr Boutsalis said.
“Although the number of paraquat-resistant populations is still relatively small, many carry resistance to both glyphosate and paraquat.”
A Victorian survey in 2020 found one-third of sampled paddocks had annual rye-grass populations that tested positive for glyphosate resistance and 50 samples with resistance to Paraquat.
To help farmers combat infestations, new herbicides are being approved, including alion (indaziflam), terrain Flow (flumioxazin) and uragan (bromacil).
Dr Boutsalis said growers need to treat weeds before seeding occurs.
“The best time to tackle fence line weed control is in autumn, when the weeds are small and the weather is still warm,” he said.
Advisory body WeedSmart has recommended farmers adopt its ‘big six mix and rotate’ tactic, which requires switching between different modes of action over several years, in tandem with knockdown herbicides if emerged weeds are present.
WeedSmart advocates for sustainable weed management and has support from GRDC, major herbicide, machinery and seed companies, and university and government research partners.
More information can be found at weedsmart.org.au
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