Grains Research and Development

Date: 01.06.2000

Tackling the enemy head-on

Professor Stephen Powles, WA Herbicide Resistance Strategy (WAHRI), examines subjects in the glasshouse at the University of Western Australia. A high proportion of WA paddocks contain resistant wee

Herbicide resistance is arguably the worst enemy of many WA graingrowers and, in the northern wheatbelt, growers are taking direct aim at this major threat to profitable farming.

Information about alternative weed-control options, to ease reliance on herbicides and prevent the development of resistance, is becoming more well known. But many WA farmers still feel they are flying blind with limited understanding or access to trial results upon which to base decisions, and a subsequent reluctance to make proactive changes.

Now 50 northern wheatbelt growers will be able to help themselves, and the entire Australian grain industry, as they develop and analyse an on-farm systems approach to weed management over four years.

Coordinated by AGWEST and supported by growers and the Federal Government through the GRDC, growers will select at least one paddock for the four-year experiment.

The first step is assessing the paddock for current weed populations, level of herbicide resistance, and weed-management practices and their efficacy.

Grower groups supporting the 50 farmer-researchers will suggest farming systems that need to be included, such as the lupin-wheat rotations of the sandplain soils, and the type of weed-control techniques that should be tested.

Says project supervisor Juliet McDonald, of AGWEST, Coorow, "it is too late for the industry to act once herbicide-resistant populations have developed; the idea is to ensure growers can change their approach to weed management before they develop resistance".

That could have a significant impact on the bottom line. If a systems approach can reduce the impact of weeds on yield by 100 kg/ha, which Ms McDonald estimates it can, wheat growers could gain $18/ha, based on $180/t.

With 100 per cent adoption over the entire 2 million hectares of the northern agriculture region, that would net $9 million per year. Even at 50 per cent adoption, it equates to $4.5m.

Techniques will include chemicals mixed with cultural control options such as weed seed collection, crop-topping, green-manuring, crops as competitors, tillage and burning.

Available tools include the decision support system Ryegrass Integrated Management (RIM), which not only will help the growers plan their approach, but will provide critical evaluation.

Many WA paddocks have resistant weeds

The growers also plan to liaise with researchers working on the WA Herbicide Resistance Initiative (WAHRI), based at the University of WA.

Led by resistance 'guru' Stephen Powles, projects at WAHRI aim to determine the overall levels of herbicide resistance of various weeds in WA, and what options, chemical or otherwise, are available for control.

Results already show that a high proportion of WA paddocks contain resistant weed populations, and that major regional differences are evident.

The northern wheatbelt has been identified with resistance 'hot-spots', which increases the value of results from this new project.

Professor Powles said a random WAHRI survey last year found that 21 per cent of wild radish plants collected from wheat paddocks in the northern agricultural region were resistant to Group B herbicides such as chlorsulfuron and triasulfuron.

"This is a massive number, indicating that the Group B herbicides are unlikely to continue to be effective on wild radish and then other broadleaf weeds," he said.

Ryegrass muitiple- resistant

Throughout WA's wheatbelt, the WAHRI random survey found that herbicide resistance in ryegrass was very high.

Within intensive cropping areas such as Wongan Hills, it found 80 per cent of ryegrass was resistant to both Group A and Group B herbicides.

"These are by far the world's highest levels of resistance and are further complicated by the fact that many populations are multiple herbicide-resistant," Professor Powles concluded.

Programs 3.5.3, 3.3.3

Contact: Ms Juliet McDonald 08 9952 1222 Professor Stephen Powles 08 9380 7833