Resistant weed headaches growing, survey shows

New survey says 43 per cent of farmers now believe they have herbicide-resistant weeds, but the number who report using more than one mode of action is falling

More Canadian farmers are reporting herbicide-resistant weeds, according to a new poll.


Nearly two-thirds of the 500 farmers surveyed in a poll conducted for BASF Canada said weeds in their fields are getting tougher to control, and 43 per cent said they suspect they have weeds resistant to herbicides. In a similar poll conducted a year ago, the number of farmers who figured they had resistant weeds was 37 per cent.


“The needle is moving,” says Joel Johnson, BASF Canada’s herbicide brand manager. “Resistance is an issue and it is not going away. More and more growers are becoming aware and their perceptions are changing.”


Most surprisingly, the survey also found fewer growers said they were using multiple modes of action to combat the problem — 67 per cent said they use herbicides from more than one group to manage their weeds. That’s 10 percentage points lower than in the poll done in March 2012.


Many farmers who rely on just one mode of action may be putting too much faith in the herbicide industry’s ability to come up with new products to keep resistant weeds at bay, said Nasir Shaikh, Manitoba’s provincial weed specialist.


“Good farmers are more cautious about using herbicides in a way that is sustainable,” he said. “But there are those who are not very sharp on rotating herbicides and the crops themselves.”


Using the same herbicides again and again is just asking for trouble because even the biggest industry players don’t have many new chemistries in the pipeline. Those that are coming out are generally pre-mixes or new twists on old chemistries, mainly because the cost of research and new registrations has soared to as high as $150 million just to have a single new product approved, he added.


But the poll’s finding may actually be good news, said Johnson.


He said he believes it’s a sign that more farmers are taking the issue of herbicide resistance more seriously.


“It’s people going back into their chemical records and saying, ‘You know, those are both Group 1s. I thought they were different groups because they had different herbicide names,’” he said.


This year, 47 per cent said glyphosate alone is no longer effective for controlling weeds. That’s a seven-percentage-point rise from a year ago.


Among the glyphosate-resistant weeds to appear in recent years are kochia in the Prairies, and Canada fleabane and giant and common ragweed in Ontario.


Shaikh said field edges are one overlooked risk factor. Common ragweed in such spots may get hit with only one-quarter of the recommended rate, survive, and then set seed later that summer.


Between 2010 and 2015, BASF Canada plans to introduce eight new active ingredients and 25 new products to aid in the fight against tough weeds. 


But that doesn’t mean farmers should be counting on new chemistries alone to solve the problem. Johnson said a game changer like glyphosate hasn’t been found — and may never materialize.


“Realistically, we don’t have anything like that and farmers need to be more proactive about resistance,” he added.


But Gary Martens, a professor at the University of Manitoba, said he fears that’s not happening.


“It’s human nature to not change the way we do things until the way we do things doesn’t work anymore — that’s just the way we are,” said Martens. “(Glyphosate) is too cheap and it’s still working.”


There’s a history of farmers overusing “silver bullets” until their effectiveness is lost, said Martens, pointing to a 2002 book by Clint Evans called The War on Weeds in the Prairie West.


It notes, for example, that in the 1930s, summerfallow was hailed as the saviour of farming until its negative aspects became impossible to ignore. Then in 1945, 2,4-D saved the day just as farmers were ready to walk away from fields choked with weeds. 


“Then we wanted to reduce tillage due to soil erosion and along came glyphosate,” said Martens. 


Technological saviours come along when almost all hope is lost, and Martens said he suspects that the chemical industry will deliver yet another reprieve. 


“Actually, I wish it wouldn’t because then we would have to use more knowledge-based farming,” said Martens, adding that in some parts of Australia, farmers have already been forced by glyphosate-resistant ryegrass to adopt a “wheat-sheep-wheat” rotation.


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