The list of herbicides that are losing their effectiveness against kochia is growing, leaving fewer tools to control the rapidly-evolving tumbleweed in soybeans.
As of 2024, kochia populations in the Canadian Prairies/Northern U.S. Plains region have shown resistance to herbicides in Groups 2, 4, 5, 9, and 14, with some plants showing combined resistance to at least three of these chemistries.
The most impactful development for growers is the resistance to glyphosate that has exploded in the last few years, but the loss of herbicides in Groups 4 and 14 is also creating challenges, says Kim Brown, weed specialist with Manitoba Agriculture, in this new Soybean School episode.
“We know that we’re starting to lose our dicamba and our fluroxypyr. Those are two Group 4 products that we’ve used very extensively in the past. And we know we’re starting to lose our Group 14s as well, which is really new, just in the last year or two,” she explains, following a presentation on weed control in soybeans at the 2024 Manitoba Crop Diagnostic School in Carman, Man. (continues below)
As glyphosate resistance has become more common, there’s been more reliance on Group 14 herbicides to clean fields prior to emergence in spring. Brown notes research in Minnesota has shown possible differences between soil-applied and foliar Group 14 products — that resistance appeared to happen quicker with foliar chemistries.
For soybeans, that leaves contact herbicides, specifically glufosinate, as an important tool for managing kochia, says Brown.
“We don’t really have much else left,” she notes, emphasizing the key with contact herbicides is to have high water volume, good water quality, the right nozzles, and right conditions.
Beyond that, Brown says the keys to kochia control in the future will continue to include crop rotation, adequate seeding rates, the right cultivar choice, row spacing, and other non-chemical means for out-competing weeds.
Related:
Soybean School: Did the weeds die? The critical weed-free period in soybeans
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