WEED surveys and herbicide testing results across Australia are consistently confirming that herbicide resistance in economically important crop weeds is increasing and spreading.
Despite some variation between states and regions, the trends are remarkably similar.
Charles Sturt University senior technical officer John Broster leads the weed survey project in NSW and has just finalised the results of the 2016 survey.
“We gathered samples from the northern NSW and plains regions in 2016, which means we have survey results from across the major graingrowing regions of NSW,” he said.
“The target weeds we collected and tested for herbicide resistance were annual ryegrass, wild oats, sowthistle, barley grass, brome grass, wild radish and Indian hedge mustard.”
The weeds were tested for their susceptibility to the major herbicide groups used for their control.
“Across NSW, the extent of ryegrass resistance to Group A ‘fops’ and Group B ‘SU’ herbicides is by far the highest, with about 60 per cent of samples being resistant, and 46pc of samples being resistant to Group B ‘Imi’ herbicides,” he said.
“There was less extensive resistance to the Group A ‘dims’ and Group D herbicides at 10pc and 11pc of samples, respectively.
“When we looked at cross-resistance in the ryegrass samples collected in NSW we found that while 24pc of samples were susceptible to all five of the major herbicide groups used for ryegrass control, a huge 43pc were resistant to three or more of these five herbicide categories.”
The surveys illustrated the cross-resistance that existed in paddocks across NSW and in other states throughout Australia.
Mr Broster presented the latest survey results at a recent WeedSmart forum in Wagga Wagga, NSW, where 170 growers, agronomists and researchers compared notes and experiences about a whole raft of weed management tools, some largely untested but showing promise in the field.
Harvest weed seed control options were of great interest, as were the demonstrated benefits of double-break cropping, utilising livestock in mixed farming enterprises and ways to extend the effective use of herbicides.
The ‘Big 6’ WeedSmart tactics known to drive down weed numbers and reduce the impact of herbicide resistance were: rotate crops and pastures; mix and rotate herbicides; increase crop competition; use the double-knock; stop weed seed set; and implement harvest weed seed control.
“Herbicide resistance can’t be beaten with herbicides alone,” Mr Broster said.
- Details: weedsmart.org.au
