The Graham Centre for Agricultural Innovation has quantified the link between cropping practices and herbicide resistance to ryegrass in each local government area across the Australian wheat belt.
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Charles Sturt University researcher, Dr John Broster, said the university has managed commercial herbicide resistance testing since 1991 and between 2001 and 2015 has analysed over 4500 annual ryegrass samples collected across southern Australia.
For this project they combined their testing results from this time period for each shire, with responses from an ABS Agricultural Service Data surveys.
Dr Broster said what they found was what farmers had long suspected - if you grow a lot of one crop you are more likely to see resistance to specific herbicide groups.
"For example, those shires that grew a lot more wheat were nearly in some cases, twice as likely to have Group A herbicide resistance than others, whereas they were less likely to have Group C or Group M resistance," Dr Broster said.
"A lot of it is logical but we've put some numbers on it, it's a bit like when yield monitors came out in headers, every farmer knew there was variation in the paddock they just didn't know how much."
He said they realised they couldn't simply tell farmers to rotate their herbicides to avoid resistance build up, with a number of management practices impacting their ability to do this.
"Cultural practices, including the choice of crop species, cultivation and management of crop residues, plus the soil pH influence the choice and use of herbicides and thus can either directly or indirectly influence the development of resistance over time," he said.
Graham Centre plant systems research pathway leader, Professor Jim Pratley said the research did clearly show that farmers should be using a range of diverse methods to control weeds.
"We don't want to lose good herbicides because of poor management," Professor Pratley said.
Professor Pratley encouraged farmers to use a range of the non-chemical resistance methods that are available.
"There are numerous options, from early sowing to get crops up vigorously so they're more competitive to reducing the number of seed that goes into the seed bank to stop weeds going through their usual life-cycle," he said.
