For as long as agriculture has existed in Western Canada, farmers have been waging a battle to control yield-robbing weeds in their fields.
It will be a similar story in 2023. The difference this time around is that battle could be shaped largely by the location where it is being fought.
While Manitoba received significant moisture last season, many parts of Saskatchewan and Alberta remained dry and continue to deal with the effects of moisture deficits from the previous couple of seasons.
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Grainews recently spoke with experts in the three Prairie provinces about the weed outlook for this year and what growers should know as they prepare for the coming season.
Manitoba
Kim Brown-Livingston, a provincial weeds specialist with Manitoba Agriculture, says a decent amount of rainfall last summer means fields in Manitoba are in pretty good shape heading into 2023. As far as weeds are concerned, it will be a relatively “normal” year, she explains.
“I think we’re getting closer to normal, like what we would expect to be seeing with normal conditions and needing those burnoffs and pre-emergent herbicides for residual weed control, and getting back into the habit of using those,” she says.
“A lot of that had dropped off the table because it was just so dry (previously) that we weren’t seeing enough weed growth to justify using those (herbicides).”
Brown-Livingston says two weeds that should be on everyone’s radar in Manitoba are waterhemp and Palmer amaranth. Both are relatively new threats in the province and are members of the pigweed family.
Waterhemp is like redroot pigweed “on steroids,” she says.
It’s much taller (up to eight feet tall), produces a lot more seeds and is a much more aggressive plant than most pigweeds. Brown-Livingston says it poses a great risk to row crops, in part because there is ample space for it to grow between rows before a canopy cover develops. There are also limited herbicide options for many row crops.
Further complicating things is the fact that waterhemp is believed to have come to the province from Eastern Canada or the northern United States pre-loaded with resistance to several herbicide groups including Groups 2 and 9.
“If this weed shows up and you were trying to spray it, you could have little or no success,” she says.
There haven’t been many reported cases of Palmer amaranth in Manitoba to date, but Brown-Livingston says growers must remain vigilant. It can grow to be even bigger than waterhemp, can be more aggressive and can develop resistance very quickly.
One of the problems with waterhemp and Palmer amaranth, Brown-Livingston notes, is by the time farmers notice it in their fields it’s often too late to spray, even if some herbicides could still control it.
The good news is that a strong, competitive crop can quickly cover the ground and prevent waterhemp and Palmer amaranth from getting a head start.
Any discussion about weeds would be incomplete without a mention of kochia. Brown-Livingston says the dry, salty soil in most of the province during the previous two years created ideal conditions for kochia.
Now that the province seems to be emerging from its latest dry cycle, she expects to see those saline areas shrink and more competitive crops grown. This could slow the spread of kochia in fields where it’s already present and prevent it from spreading into new areas.
Canada fleabane, also known as horseweed, has been around in Manitoba for some time, but it has never posed much of a problem — until recent reports of potential glyphosate resistance.
The threat it poses to crops such as soybeans and corn could now be much higher, Brown-Livingston explains.
“We haven’t seen it resistant like it is in Ontario and the United States. It has always been something we could control, so that (resistance) is something that’s brand new and needs to be on everybody’s radar,” she says.
Brown-Livingston also notes that farmers should be prepared for a return of perennial and winter annual weeds as the province appears to be entering a more normal or possibly wetter moisture cycle.
Saskatchewan
Clark Brenzil, a provincial weed control specialist with the Saskatchewan Ministry of Agriculture, says soil moisture shortages will likely continue in many parts of the province that went into last fall without soil moisture reserves, particularly on the western side of the province.
Despite the dry conditions, the weed threat will remain significant, Brenzil suggests. He says that could be particularly true with kochia, Russian thistle, green foxtail, lamb’s quarters, wild oats and pigweeds, which tend to be better adapted to hotter, drier conditions and “get up out of the ground quickly.”
“Generally, whatever weeds have been growing in your fields the last couple of years, they are likely the ones growing there this year,” he says.
Although waterhemp and Palmer amaranth aren’t a major concern in Saskatchewan yet, Brenzil says provincial officials are “keeping an eye out for them,” since they have been detected near the province’s borders to the east from Manitoba and to the south from North Dakota.
Brenzil says growers should take note of any pigweeds that pop up above crop canopies such as lentils and soybeans and appear to be significantly larger than normal after an in-crop weed control pass.
If farmers are concerned waterhemp or Palmer amaranth may be present in their fields, he suggests contacting an agronomist or one of the province’s regional specialists to investigate the site and collect weed samples for proper identification.
Alberta
Although the soil moisture situation in Alberta was better heading into 2023 than it was last year, there remains what has been called an “island of dryness” in areas around the city of Calgary including Airdrie and Red Deer.
Charles Geddes, a research scientist with Agriculture and Agri-Food Canada (AAFC) based in Lethbridge, says while it’s difficult to predict which weeds will be the most problematic during the upcoming growing season, kochia and Russian thistle are likely to remain a concern in southeastern areas of the province with drier soil.
Wild oats have been an issue in Alberta for some time and Geddes says it’s likely to be an issue again this year.
One of the newer weed threats in Alberta is glyphosate-resistant downy brome, which was first confirmed in southern Alberta in 2021.
Geddes says the province doesn’t yet know the extent of the problem and hasn’t been contacted by many farmers or agronomists who suspect they may be dealing with the weed.
“We’re hoping it’s a localized case and it won’t spread from there, but we haven’t done a survey yet to know how widespread the issue is,” he says, adding that downy brome is a problem mostly associated with winter crops such as winter wheat.
Although pigweeds, such as redroot, green and smooth pigweeds, have been present in Alberta for a while, newer species such as waterhemp and Palmer amaranth have yet to show up in the province. However, Geddes says there are concerns they could potentially arrive in Alberta as growing seasons become longer.
“It’s likely they’ll eventually make their way to Alberta, but it would be surprising if it did happen that quickly,” he says. “But we do know they’re on the Prairies and they’re likely spreading.”
Herbicide carry-over risk
While the weed threat will vary from region to region in 2023 in part because of soil moisture levels, the same holds true when it comes to herbicide carry-over, since herbicide breakdown is largely governed by a combination of moisture and warm temperatures.
Based on soil moisture maps for the 2022 growing season, while the majority of herbicide residue degradation would occur prior to spring 2023, Geddes says the southeast corner is the area of greatest concern for herbicide carry-over in Alberta.
However, he said precipitation can be highly variable from field to field and farmers should consider how much precipitation they received last year in comparison with an average year to determine their levels of risk.
Farmers should also review the re-cropping restrictions of any residual herbicides they used in 2022 and to check with manufacturers to determine if there have been any updates issued for the coming growing season.
Brown-Livingston says Manitoba is in “better shape than we have been in years” when it comes to the risk of herbicide carry-over, thanks to a return to more normal precipitation levels.
Still, she recommends farmers not take the situation for granted, especially if their fields are located in an area that received less-than-normal rainfall. She also suggests growers check label recommendations for any herbicides they used last year, which are also available in the province’s annual crop protection guide.
In Saskatchewan, the risk of herbicide carry-over is still relatively acute on the western side of the province, although not quite as severe as it was last year, Brenzil says.
The eastern side of the province is in good shape, he adds, since it received a significant amount of rainfall early last season.
His advice to growers who may be concerned about herbicide carry-over this season is to be conservative about their crop choices and go with longer rotation periods.
Brenzil also recommends growers be conscious of the quality of the water they mix with their herbicides this coming season. One of the results of last year’s glyphosate shortage was many farmers resorted to using reduced rates, which in combination with antagonism from water quality resulted in the product not working as expected.
He suggests farmers get their water sources tested early in the season to make sure they know the level of water hardness they are dealing with.
“You want to make sure you’re getting the most out of a product you (use),” he says.
Herbicide resistance
Herbicide resistance is on the minds of farmers, agronomists and researchers across the Prairies this season.
Herbicide-resistant weeds are estimated to cost western Canadian farmers as much as $530 million annually in lost yields and alternative weed management practices.
Numbers from Manitoba’s latest herbicide-resistant weed survey conducted in 2022 are expected to be released this fall. It will likely show that kochia remains one of the worst herbicide-resistant weed issues in the province.
Brown-Livingston says herbicide-resistant kochia is a widespread problem in Manitoba and the number of acres where it has been detected continues to grow.
“The resistance is increasing, and we need to be watching,” she says, adding herbicide resistance in wild oats continues to be an area of concern.
Another issue in Manitoba, according to Brown-Livingston, is weed resistance to the Group 9 herbicide glyphosate.
To tackle this problem, growers can tank mix other products with glyphosate whenever possible. Adding more complexity to herbicide mixtures can help slow the development of resistance. She also points out the most effective tool in slowing herbicide resistance is growing competitive crops.
In Alberta, there is concern about possible resistance to protoporphyrinogen oxidate (PPO) inhibitors, or Group 14 herbicides, in kochia.
Geddes says growers should watch for activity in their pre-plant burndowns if they’re using Group 14 products.
Indication of a problem is when kochia plants that have been hit with herbicide remain alive next to others that are dead. Geddes recommends farmers contact him about herbicide-resistant weeds because his lab is working to characterize the issue in the Prairies.
Another herbicide-resistant weed concern in Alberta, according to Geddes, is wild oat resistance to Group 1 and 2 herbicide products, which is a widespread and continuing issue for many farmers.
Brenzil says herbicide resistance has been on an upward trajectory in Western Canada since the 1990s and isn’t likely to change anytime soon unless producers make significant changes in how they manage their crops and their weeds.
In Saskatchewan, the most recent herbicide-resistant weed survey showed 87 per cent of kochia plants sampled appeared to be glyphosate resistant. High levels of dicamba and fluroxypyr resistance have also shown up in recent Alberta surveys, he adds.
“We’re closing doors one at a time to be able to control that weed,” he says.
A shift in thinking is needed about how kochia and other herbicide-resistant weeds are managed.
“Even though we have all of these new technologies that are making things easier for us, it’s also making things easier for some of these weeds to be more problematic in the system,” he explains.
“One of the things that we’ve done that has made life a little easier for kochia is that we’re always entertaining reducing our seeding rates (and) we’re always pushing our row spacing out rather than bringing it back in to the standard that has been around since time immemorial, which is six to eight inches for row spacing.”
