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7-Misc: Increasing number of weeds develop herbicide resistance

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TITLE:  Herbicide resistance in Australia a "wake-up call" for
SOURCE: Manitoba Co-operator, Canada
        from a Lethbridge Research Centre press release
        sent by AGNET, Canada
DATE:   June 10, 1999

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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

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