Annual ryegrass may win the battle of the weeds, leaving farmers without effective chemical control, if the use of trifluralin is not managed better.
Weed scientists warn that if current trends continue, widespread resistance to trifluralin in southern Australia is likely in less than a decade.
Trifluralin resistance in annual ryegrass has been identified across southern Australia, including Western Australia.
Researchers say the dinitroalanine herbicides, including trifluralin, are too valuable to waste and must be treated as carefully as Group A and B herbicides.
Producers have turned back to trifluralin because of ryegrass resistance to Group A (Fusilade, Verdict, etc.) and Group B (Glean, Logran) herbicides and because trifluralin has proven successful in no-till cropping.
"Producers running a cereal, canola and pulse rotation can be easily tempted to use trifluralin year after year but history has shown with herbicides, when you're on a good thing, DON'T stick to it," said Steve Sutherland, weed extension agronomist for NSW Agriculture.
Mr Sutherland's concern is seconded by visiting weed scientist Bob Blackshaw from Agriculture Canada, recently returned from a tour of South Australia where trifluralin is used heavily.
"They're setting themselves up for a resistance problem, using trifluralin every year in their wheat, barley and canola rotations," said Dr Blackshaw.
He said farmers in Canada face widespread resistance in green foxtail (Setaria sp.) and wild oat to trifluralin following 10 to 15 years of regular use.
Given the lack of herbicide options, Dr Blackshaw believes Australian producers "will have to look at other ways of controlling weeds.
"Producers should consider more diversity in their crop rotations, using more forages, for example, and cutting them for hay or silage. Increasing seed rates is another example of successful non-chemical weed control techniques, " Dr Blackshaw said.
Research by NSW Agriculture and elsewhere, under the umbrella of the Cooperative Research Centre for Weed Management Systems and with GRDC support, is examining a whole range of weed management techniques which can reduce producer reliance on herbicides.
Program 3.3.2 Contact: Dr Deirdre Lemerle or Mr Steve Sutherland 02 6938 1999
North, South, West