Canadian farmers must take immediate steps to reduce reliance on herbicides or face an increasing weed-resistance problem similar to what is happening in Australia, says a veteran weed scientist from the Lethbridge Research Centre. He is part of a new research study under way to help producers by providing specific weed management strategies. Dr. Bob Blackshaw recently returned from a one-year work transfer in Australia, where he observed that country's widespread herbicide resistance problem. He says many Australian farmers have no herbicide options left for some major weeds and have been forced to dramatically change how they farm.

Canadian farmers could face the same situation. In recent years, there has been growing awareness of the threat of herbicide resistance and wide promotion of preventive strategies such as herbicide rotations, but not all producers are taking action. In addition, the Australian example shows that herbicide rotations are not the sole solution; continued reliance on herbicides has led to resistance to many different control products. Combining herbicides with agronomic practices that allow crops to outcompete weeds may be the answer to long-term weed management.

"The Australian example should be seen as a wake-up call," says Blackshaw. "Don't wait until you're forced into a crisis situation. Try and be proactive by adopting better ways of managing your crop." According to Australia's Grains Research and Development Cor-poration, herbicide resistance is reported to affect up to 10 per cent of the country's cropping area. The main problem is resistance to Group 1 and 2 herbicides among populations of annual ryegrass, which is Australia's major problem weed, comparable to wild oats in Canada.

"Some populations are now resistant to five different herbicide groups, leaving farmers with their backs to the wall," says Blackshaw. Most recently, several populations of annual ryegrass were found to be resistant to glyphosate (trade names Roundup and Touchdown), a development that severely threatens conservation tillage in Australia. In Canada, though many farmers understand the long-term benefits of improved management, short-term economic concerns and a lack of specific strategies are obstacles to change, he says. But further research could help the situation. A new integrated weed management project was started at several Prairie research centres last year to help farmers by providing baseline strategies for reducing herbicide use while maintaining optimum crop yields. The project is headquartered at Agriculture Canada's Lethbridge Research Centre and also includes research at the Lacombe Research Centre and Scott, Saskatchewan research site. The Brandon Research Centre may also join the project next year.

"We know that certain rotations, seeding practices and fertilizer applications can improve weed management and consequently reduce the need for herbicides," says Blackshaw, co-ordinator of the roughly six-year-old project. "But what makes this study unique is it will look at all of these factors in different combinations, in the overall context of their effect on production, including an economic assessment of these practices.

That will help producers decide which strategies are likely to be the most effective on their farm and help our industry in Canada prevent the herbicide-resistance problems we see in other parts of the world." In Australia, Blackshaw worked on an integrated weed management study at a local research centre in Wagga Wagga, New South Wales. He also took the opportunity to observe how farmers are responding to the herbicide-resistance problem and develop ideas that could be incorporated into the Canadian project. Australian producers have adopted improved management techniques such as using more plowed-under "green manure" crops and short-term forages, harvesting crops as silage before weeds set seed and collecting weed seed coming out of the back of the combine.

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