The results of a 1997 survey of herbicide-resistant wild oat in two Saskatchewan townships show that the populations of this weed have increased in number, distribution and diversity since the province-wide survey of 1996. This news comes as no surprise to the provincial weed control specialist, Saskatchewan Agriculture and Food (SAF) Clark Brenzil. "According to the Crop Protection Institute (CPI), herbicide expenditures increased by about 50 per cent in Western Canada from 1994 to 1998. Furthermore, at 36 per cent of national sales, Saskatchewan has the highest sales of herbicides in Canada," says Brenzil.
"So cases of herbicide resistance are continuing to increase, whether we quantify it or not. The survey merely shows the problem that results from reliance on a single management tool to deal with weeds. It highlights the critical nature of herbicide resistance in this province. Producers need to proactively look for the problem and take measures to keep it from spreading in their fields," says Brenzil.
The 1997 survey was carried out by Agriculture and Agri-Food Canada's (AAFC) Saskatoon Research Centre to test a different survey method, and to confirm the 1996 finding of higher herbicide resistance in the Parkland region. It was based on a systematic survey of fields in two randomly selected townships: one in the Parkland, or black and grey soil zone; and the other in the Grassland region, or brown and dark brown soil zone.
"We found that the populations of herbicide-resistant wild oat is higher than was documented in 1996 and that fields have more combinations of resistance: for example, more than half the fields in both both townships had some herbicide resistance, and many of the fields were resistant to two or more groups of herbicides," says Dr. Huch Beckie, a AAFC research scientist.
As in 1996, the Parkland had higher levels of herbicide-resistant wild oat than the Grassland region. This is because the Parkland climate is conducive to more continuous cropping, which means more herbicide use, says Beckie. One significant finding was the difference in incidence between herbicide-resistant wild oat on land bases of different sizes: producers with a large land base had a higher incidence of Group 1 or 2 herbicide resistance than producers with less land.
"Because there was no herbicide history done with this survey, we're not sure of the reason behind this finding," says Beckie. "It could be because the producers are spreading the seed as they travel from field to field, or because they use more herbicides."
He says farmers with multiple-group resistance will have to be especially careful to safeguard the effectiveness of the remaining selective and non-selective herbicides by using them conservatively in conjunction with cultural weed management practices.
"With the confirmation of glyphosate-resistance annual ryegrass in Australia, we know that no herbicide on the planet is immune to the development of resistance," adds Brenzil.
"The bottom line, of course, is to use less herbicides and more cultural weed management practices such as crop rotation, and increased crop seeding rates. This advice applies to all farmers; prevention of herbicide-resistant weeds is far easier than eliminating them."
Other measures that producers can take include: the use of narrow row spacings; cleaning equipment thoroughly before leaving fields; banding fertilizers to benefit only the crop; using chaff collectors to prevent seed from returning to the field, using selective tillage to deal with problem patches; and maintaining good records to facilitate rotations of crops and herbicides
More information on preventing or dealing with weed resistance may be found in the annual SAF publication Guide to Crop Protection at all Rural Service Centres.
For more information, contact:
Dr. Hugh Beckie, Research Scientist
Widespread herbicide-resistance in Australia a "wake-up call" for Canada
Lethbridge, AB, May 12: Canadian farmers must take immediate steps to reduce their reliance on herbicides or face an increasing weed resistance problem s imilar to what is happening in Australia, says a veteran weed scientist from the Lethbridge Research Centre. He is part of a new research study underway 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 preventative 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 out-compete 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 Corporation, herbicide resistance is reported to affect up to 10 percent of the country's cropping area. The main problem is resistance to group one and two herbicides among populations of annual ryegrass, which is the number one weed problem in Australia, comparable to wild oats in Canada.
"Some populations are now resistant to five different herbicide groups, leaving farmers with their backs against the wall," says Blackshaw. Most recently, several populations of annual ryegrass were found to be resistant to glyphosate (trade names Round-Up 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 and Agri-Food Canada's (AAFC) Lethbridge Research Centre, and also includes research at AAFC's Lacombe Research Centre and Scott, Sask., 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, coordinator of the roughly six-year 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 effects 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 ploughed 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.
The Lethbridge Research Centre is a leading institution for agricultural sustainability research in Western Canada, with major sections in crop sciences, land resource sciences and livestock sciences.
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Last Updated on 3/13/00
By Karen Lutz