After a series of dry years on the Prairies — with 2021 being driest of all — the provincial weed outlook for 2022 is varied across Western Canada and field to field. From kochia invading new territory to a possible increase of overwintering weeds — such as later-emerging false cleavers, Canada thistle, shepherd’s purse and narrow-leaved hawk’s-beard — in regions that received moisture late in the growing season last year, Alberta producers have a number of potential weed issues to stay on top of this spring.
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Experts warn if Saskatchewan comes out of a dry cycle in 2022, C3 weeds, such as wild mustard and wild oat, could do better this year than the C4 weeds (kochia, green foxtail, pigweeds, lamb’s quarters and Russian thistle) that have been predominant during the dry, hot conditions of the last few years.
And, in Manitoba, due to precipitation last fall and, in some areas, many feet of snow over the winter, there may be heavy weed germination — and weed control early in the season will be critical. Below are the full details by province.
Alberta
Among serious weed concerns in Alberta is kochia, which did well without much moisture last year. “Areas where kochia were prolific may well increase infestations in 2022,” reports Shaun Sharpe, a research scientist with Agriculture and Agri-Food Canada. “New patches may be forming in new parts of the field or neighbouring fields where tumbleweeds may have blown. Approaches and compacted areas may be potential areas of invasion and spread.”
He adds glyphosate resistance is becoming widespread in kochia so growers should look at including additional effective modes of action in the tank where possible, for example, Groups 6 and 14 products.
In addition, Sharpe cautions there is a lot of kochia reproducing in Alberta along roadsides, grid roads and field margins and around sloughs. “Please consider ‘closing the back door’ by controlling (the weeds in these areas), if possible, as early as possible, and removing their opportunity to invade into farmland,” he says. “Early control is better because some herbicide-resistant traits can move in the pollen, not just with the tumbleweed.”
Saskatchewan provincial weed specialist Clark Brenzil highly recommends preventing the growth of kochia by planting perennial forages in ditches and even in saline (or otherwise non-productive) areas in fields. Please see the story “How to scout for herbicide-resistant weeds” here on Grainews for more information on this management strategy.
However, some areas in Alberta received moisture late in the growing season, and Sharpe says these regions may favour overwintering weeds such as later-emerging false cleavers, Canada thistle, shepherd’s purse and narrow-leaved hawk’s-beard.
“Canada thistle has some degree of glyphosate tolerance and, once established, it can regenerate from below ground,” he warns. “These plants should be emerging and growing early, so pre-seed burn-down may be an important herbicide timing. Depending on the degree of shatter and yield loss due to poor environmental conditions of harvest 2021, volunteer crops may be a problem as well.”
As always, Sharpe also urges growers in Alberta and beyond to watch out for “weird-looking” pigweeds — Palmer amaranth and waterhemp. Early detection of these extremely invasive weeds is critical.
Also, wild oat is a constant threat with its wide distribution and some biotypes have Groups 1 and 2 resistance. “Herbicide layering strategies will be important to control wild oat in-crop and encouraging canopy closure can help suppress later-emerging flushes,” Sharpe adds.
Saskatchewan
As expected, kochia also did well in Saskatchewan in 2021. Brenzil explains in the big picture, weed populations change on individual farms over time, and will change in terms of what’s dominant due to weather patterns. The dry conditions experienced for the last few years mean weeds with “C4” physiology have become predominant in the province. (For more information about C3 and C4 plants, check out the 2018 Grainews story called “Untangling C3 and C4 plants.”
C4 weeds, which are recognized as more tolerant to drought, such as kochia, green foxtail, pigweeds, lamb’s quarters and Russian thistle, can close off their leaf stomata (tiny openings that allow CO2 to enter) to stop water loss and utilize captured CO2 to a much lower concentration within the leaf for photosynthesis, meaning they will grow for longer through hot, dry days than “C3” or cool-season plants. However, Brenzil says if Saskatchewan comes out of a dry cycle in 2022, C3 weeds, such as wild mustard and wild oat, could do better this year.
With respect to snow, Brenzil reports while there’s ample in the northern and eastern (black soil zones) parts of the province, the southwest is still wanting for moisture much the same as southern Alberta. He says how much this snow will contribute to soil moisture levels is yet to be seen.
Whatever the growing season conditions, he reminds growers when using herbicides to use multiple modes of action and best management practices to ensure good weed control. “As always, use integrated crop management and a good seeding rate with ample fertilizer to get the crop growing well so your crop relies less on the herbicide,” he says. “Enable your crop to do most of the work.”
Manitoba
Provincial weed specialist Kim Brown-Livingston says many areas of Manitoba had a moist fall last year, which resulted in a lot of weed growth and volunteers using up moisture and nutrients. “Last fall, I recommended spraying instead of cultivating so that moisture loss wouldn’t be even worse, and some growers just let the winter kill the weeds,” she notes. “Overall, I don’t think we’re going into a lot of tillage but hopefully a clean seedbed.”
Additional moisture arrived in Manitoba this winter, which Brown-Livingston describes as “more snow than we’ve seen in years. There are feet of snow on many fields and others have at least inches of snow at this point in late February, with more to possibly come. For the first time in several years, we’ll have a lot of weed germination and we need to be ready for weed control first thing. The weed seeds are always there.”
This moisture could mean a proliferation of weeds, in general, in farmers’ fields. She recommends this year growers scout fields regularly for all weeds typically found on their farms.
Herbicide residue carry-over, as serious issue
Sharpe, Brenzil and Brown-Livingston all strongly caution growers about the increased potential for herbicide residue carry-over in 2022 due to the limited moisture in 2021.
Many herbicides are broken down by microbes in the soil and the microbes require moisture and heat to do that. In Manitoba, Brown-Livingston reports while there was some rain in early June and then late August and September, its timing didn’t help with breaking down herbicide residue in the soil there.
Crop injury from residue not only affects yield and crop growth, but weed growth can be supported if the crop isn’t competitive, says Sharpe.
Herbicide residue will also limit crop options, says Brenzil. Also, because of the dry conditions in 2020 and 2021, “growers may have to think about herbicides applied two or, even, three years ago,” he cautions. Brenzil urges growers to check with manufacturers of the residual herbicides used in 2020 and 2021 for assistance in selecting rotational crops that are more tolerant to residues of the herbicides used.
Supply chain worries
On top of herbicide resistance, residual herbicide and spring weather, growers also should be concerned about herbicide availability. “There are concerns about the supply chain for herbicides not just in North America but Asia as well,” Brenzil reports.
“Glyphosate products from Bayer and other companies could be in short supply this year. Bayer’s glyphosate production is being impacted in terms of limited availability of the ingredient caustic soda. Bayer had initially estimated a three-month delay with glyphosate production, and is trying to find alternative manufacturing options, so it’s hard to say what will happen. Growers need to have a plan A, B and C for crops and corresponding herbicide choices.”
Brown-Livingston advises growers to order herbicide, buy it and take it home as soon as they can. “Hopefully, in the spring, we’ll have enough herbicide for the spring and also for the in-season applications as well,” she says.
Like Brenzil, she warns growers to “be careful to have product for your spring burn-off products for the crop rotation you are planning. And if you have to change rotation options, be prepared with products for that.
“And don’t hoard herbicides like toilet paper. Work with your local supplier to order what you need and only what you need. There is no tolerance this year to order from multiple suppliers and then cancel a bunch of it at the last minute.”
