Farmers need to be on their toes to keep weeds in check and prevent crop injury this spring due to environmental conditions last year and those developing now. To help make the job easier for you, Grainews reached out to weed specialists in each province for their recommendations this spring season.
In Alberta, Agriculture and Agri-Food Canada weed specialists and research scientists Breanne Tidemann and Shaun Sharpe say, with respect to pulses, the use of some Group 2 chemistries, particularly when conditions are hot and humid, could increase crop injury potential post-emergence. This could be the result of increased absorption and the crop being unable to keep up with metabolism of the herbicide. They also warn producers that application timing can be fairly narrow for post-emergence products if crops are growing quickly.
In addition, Tidemann and Sharpe encourage those farmers with fields prone to winter annuals to do their staging prior to choosing burndown chemicals. If it’s really dry, check to see if anything is growing above or below residue.
In addition, consider mixing a residual pre-emergent product with your burndown for working multiple modes of action into a herbicide-layering strategy, the weed scientists recommend. Tidemann and Sharpe also advise farmers to check records to ensure they select crops compatible with what they sprayed last year, taking into consideration how much precipitation they received during the growing season.
In terms of specific weeds, the scientists warn farmers cleavers could have started growing last fall, so scouting is important as well as checking herbicide labels to make sure a product is chosen that can handle the size of cleavers in the field. And, as kochia resistance grows, Tidemann and Sharpe urge growers not to rely solely on glyphosate for their burndown treatments, but recommend a Group 14 or 6. Also, they advise farmers to keep an eye out for “weird-looking” pigweeds. Palmer amaranth and waterhemp are real potential threats to agriculture across the Prairies. They encourage farmers to report any odd-looking pigweed and have it identified.
Multiple herbicide-resistant wild oats are present in higher numbers every year across the Prairies, and with resistance to Groups 1 and 2, there are limited in-crop herbicide options. Tidemann and Sharpe advise farmers to use a herbicide-layering strategy — even if the pre-emergent products only offer suppression they can help with the management of these populations. This advice is in addition to crop rotation, seeding rate and potential mechanical control options.
Provincial weed specialist Clark Brenzil says Saskatchewan may be coming out of a dry cycle in 2021, which means that C3 weeds, such as wild mustard and wild oat, could do better this year. Similarly, those that prefer drier conditions and were predominant the last few years, such as kochia and Russian thistle, may not compete as well with crops this year.
Because the southern portion of the province’s greenbelt experienced dry conditions last year, farmers there should watch out for herbicide residues, which could cause problems with registered recropping options, adds Brenzil.
To further explain this point, Brenzil refers to the 2021 Herbicide Carryover Risk Level Maps pictured below (which can also be found at saskatchewan.ca).
“Moving from the June 2 to August 31 map to the June 16 to September 14 map, you can see the dry conditions got more pronounced and the northern extent of the risk areas for late herbicide applications went as far north as PrinceAlbert,”Brenzil says. He also urges producers to check with the manufacturers of residual herbicides used in 2020 for assistance in selecting rotational crops that are more tolerant to residues of the herbicides used.
In addition, Brenzil urges producers to be vigilant with respect to herbicide resistance. “Use integrated crop management and a good seeding rate with ample fertilizer to get the crop growing well, so your crop relies lesson the herbicide,” he says. “Let your crop do most of the work.”
Provincial weed specialist Kim Brown-Livingston says most of Manitoba had a pretty dry fall, and the weed control that farmers managed to carry out at that time will affect their management decisions this spring.
Tillage wasn’t possible in really dry areas, and some growers didn’t need to do a fall spray program, for example. “Even with dry spring conditions, we will see weeds grow, so watch for winter annuals like cleavers, narrow-leaved hawksbeard, stinkweed and shepherd’s purse. They can get really big, really fast, especially if they weren’t touched last fall and they’ve got a nice early start this spring.”
Volunteer canola will also be germinating if it hasn’t been buried by tillage. Those growers who had weedy canola fields in areas that experienced big summer rains last year, should expect more weeds than usual this spring.
In 2021, there may be more perennial weed issues in Manitoba due to the dry conditions over the last few years and the shift to less tillage to preserve scarce moisture.
For perennial weeds like foxtail barley, Canada thistle, quackgrass and dandelion, preharvest weed control followed by a post-harvest spray (if there’s regrowth) is the best plan, says Brown-Livingston. “If facing perennial weeds this spring, you won’t be able to eliminate them with a pre-burn and in-crop spray,” she says. “You need to plan for weed control the whole season to really get at them.”
Weeds to watch for this year in the province are kochia, waterhemp and Palmer amaranth. Kochia and waterhemp are confirmed resistant to Groups 9 and 2 in Manitoba, and are resistant to more herbicide groups elsewhere, explains Brown- Livingston. “Having these weeds on-farm, means implementing a long-term management strategy using other herbicide groups wherever possible,”she says. “Be diligent in scouting for new weeds on-farm. If you’re unsure, get a positive ID so you know what you’re dealing with.”
Echoing Brenzil’s advice, she recommends whatever crop you grow, grow it well. “Height, seeding rate, row spacing, fertilization — grow the best crop possible so there’s more bushels and less weeds,” she says. “Use tillage where prudent. And if there’s a place for cover crops and/or short-term forages on your farm, those are tools we can use to fight resistant weeds.”