Australia - Trifluralin resistance prompts weed warning

Grains Research and Development Corporation (GRDC) supported researcher Peter Newman has warned trifluralin resistance is an emerging problem in Western Australia which could creep up on growers.

Mr Newman, of the Department of Agriculture and Food (DAFWA), says growers can combat the problem by preventing weeds setting seed in every paddock, every year, and/or managing weed seeds at harvest.

Farmers could also test trifluralin resistance levels this harvest by sending weed seeds to a laboratory for testing.

Mr Newman has monitored integrated weed management (IWM) practices in focus paddocks for nine years as part of an ongoing GRDC study and recently confirmed developing trifluralin resistance levels in annual ryegrass in a paddock at Mingenew.

"A hint of trifluralin resistance was detected in the paddock in 2008, then developing resistance levels were confirmed after trifluralin was applied in 2009 – with 14 per cent of weeds proving resistant to the herbicide,” he said.

"With the amount of trifluralin being put on to paddocks in recent years, due partly to cheaper prices, I think we are going to come up against a big problem with trifluralin resistance in the future.”

A 2003 survey conducted by the WA Herbicide Resistance Initiative (WAHRI) and supported by the GRDC found 24% of weed samples tested had low levels of resistance to trifluralin, which equated to 5-10 per cent weed survival at recommended rates. WAHRI plans to conduct another survey in WA this year.

Trifluralin resistance is already widespread in South Australia.

Mr Newman said growers should assume they already have resistance and stop weeds setting seed to keep trifluralin resistance at bay.

"IWM is all about stopping weed seed set in every paddock, every year, and/or managing weed seeds at harvest time,” he said.

"Growers using any herbicide need to think about which IWM practice will follow - whether it be crop topping, using a chaff cart or burning windrows.”

Mr Newman said trifluralin resistance could emerge gradually in paddocks, increasing in strength slightly each year.

He said the Mingenew paddock with trifluralin resistance is on sandplain soil and has a long cropping history.

It has a history of trifluralin use, but not every year.

"This is a wakeup call – if we wait for a full blow out of trifluralin resistance in the WA grainbelt there will be high numbers of trifluralin resistant ryegrass,” Mr Newman said.

Growers can obtain information on integrated weed management and herbicide resistance through GRDC’s Weedlinks website at www.grdc.com.au/weedlinks

Source: fw.farmonline.com.au