Western Canadian farmers will have a tough time battling the next glyphosate resistant weed, says an expert.
Wild oats is the most likely candidate to follow resistant kochia, according to a risk assessment model developed by Hugh Beckie, a weed scientist with Agriculture Canada.
The same model successfully forecast kochia as Western Canada’s first glyphosate resistant weed.
The forecast came out in 2010, one year before the weed was discovered in a field in southern Alberta. It has since been detected in Saskatchewan and Manitoba.
Kochia is the only glyphosate tolerant weed in Western Canada, but the U.S. experience suggests others are sure to follow.
“Wild oats resistant to glyphosate would be a worst-case scenario,” Beckie said in an interview following his presentation at the 2014 Canola Discovery Forum.
“It’s really resistant to everything out there already. If you lose the efficacy of glyphosate, you really restrict your herbicide options to control that weed.”
Wild oats has a resistance risk assessment rating of 9.99 in the brown and dark brown soil zones (grassland region) and 7.83 in the black and grey soil zones (parkland region).
It is followed by green foxtail with a 6.54 rating in the grassland and 4.09 rating in the parkland.
Cleavers are expected to be a close third in the parkland with a 4.05 rating. Wild buckwheat is the fourth likeliest candidate in the parkland at 3.01 and the third likeliest in the grassland at 2.71.
Beckie said wild buckwheat’s risk rating will rise dramatically with the anticipated 2016 introduction of Monsanto’s TruFlex Roundup Ready canola.
Wild buckwheat is more tolerant to glyphosate than other annual weeds. It is hard to control at today’s recommended application rates.
TruFlex canola will allow growers to use higher rates of the chemical over a wider window of application.
Monsanto’s new Roundup Ready trait will make the weed more susceptible to the most popular herbicide used in Western Canada, but it will also increase resistance selection pressure in weed populations.
“The risk rate is going to increase substantially, and it is our most abundant weed, so that’s one to watch,” said Beckie.
Joe Vink, weed management technical lead with Monsanto Canada, doesn’t think higher rates of herbicide and a longer window of application will result in glyphosate resistant buckwheat.
“I don’t think that necessarily drives the evolution of glyphosate resistance,” he said.
“For me, it’s more the frequency of application and just total over-reliance on one herbicide mode of action.”
Vink said growers need to use best management practices such as crop diversification and tank mixing to combat the resistance problem.
“It would be really, really nice if we had other herbicides available in canola to tank mix with Roundup Ready, but there are very limited options at this point,” he said.
Beckie said the last new herbicide mode of action was 32 years ago and a new one is at least another 10 years away.
Canola has been a key weapon in combatting weed resistance in Western Canada. Canola hybrids are good at fighting weeds, and the herbicides used on canola contain two modes of action that are not used widely in other crops: glyphosate and glufosinate.
Glyphosate resistance is a serious threat to western Canadian crop production because growers rely so heavily on the chemical. More glyphosate was sold in Western Canada in 2012 than the next 12 most popular active ingredients combined.