Glyphosate-resistant kochia still appears to be relatively rare in Manitoba, but that’s no reason for farmers to become complacent, the provincial government’s weed specialist says.
In fact, the situation calls for more vigilance, rather than less, Jeanette Gaultier, weed specialist with Manitoba Agriculture, Food and Rural Development (MAFRD) said.
Glyphosate-resistant kochia was confirmed in just two of 283 Manitoba fields in 2014 from samples collected in 2013.
Earlier this year MAFRD asked agronomists to submit samples of suspected cases of glyphosate-resistant kochia so they could be tested for free in the new Pest Surveillance Initiative (PSI) lab. The lab has a quick test eliminating the need to grow the kochia to determine if it’s resistant or not, Gaultier said. However, very few samples were submitted.
“If people had suspect samples I think they would have sent them in,” she said. “I think it’s a positive sign, but I don’t think it’s a good reason for us to be slack on our resistance management, because it did pop up in the official survey that Hugh Beckie (of Agriculture and Agri-Food Canada) did. We know that it is there. Even if it is at low levels we might as well manage for it.”
Five per cent of Alberta and Saskatchewan fields surveyed in 2012 and 2013 had glyphosate-resistant kochia, Beckie said in an email Sept. 17. It’s more common in those provinces because there’s more chemfallow. More kochia is exposed on a regular basis to glyphosate resulting in more selection for glyphosate-resistant types.
The location of Manitoba’s two cases has not been disclosed but it wasn’t in western Manitoba. It’s suspected the resistant weed seed came in from North Dakota.
It’s assumed almost all kochia in Manitoba is already resistant to Group 2 herbicides, making glyphosate-resistant kochia more complicated to control.
Kochia is a flushing weed so it’s hard sometimes to determine whether a patch was missed by a glyphosate application or is in fact resistant, Gaultier said.
The PSI lab hasn’t tested the few samples that have come in, but will soon, she said.
The lab has also received glyphosate-resistant kochia seed from Agriculture and Agri-Food Canada, which the lab will grow and test to be sure its test is working properly.
Farmers and agronomists are still encouraged to submit samples of kochia suspected of being glyphosate resistant and get them tested for free, Gaultier said. To do so contact your local MAFRD GO office.
The PSI lab expects to charge a fee for the test next year.
Farmers should rotate their herbicide groups and tank mix different groups to delay the onset of herbicide-resistant weeds, Gaultier said. However, spraying kochia with glyphosate in the fall doesn’t add much to the selection pressure because seed has already been set, she said.
Manitoba is no stranger to herbicide-resistant weeds, with Group 3-resistant green foxtail first identified in 1988. However, glyphosate-resistant weeds are relatively new to Canada. The first documented case was giant ragweed in Ontario in 2009 followed by Canada fleabane in 2011, also in Ontario. But weed scientists fear it’s just the beginning, unless farmers take steps to mitigate it.
Herbicide-resistant weeds are the product of natural selection. Most weed populations have some biotypes that are naturally resistant to a certain herbicide. As the population of susceptible weeds declines the resistant ones are left to multiply.
The popularity of Roundup Ready (glyphosate-resistant) crops, along with glyphosate’s effectiveness as a non-selective herbicide and low cost has seen a steady rise in its use, including multiple applications in the same fields year after year.