Key facts
- Cool spring conditions have delayed weed emergence in Manitoba.
- Herbicide-resistant weeds such as kochia, wild oats, waterhemp, and Canada fleabane are a concern.
- Kochia exhibits resistance to Groups 2, 9, 14, and some Group 4 herbicides.
- Waterhemp is spreading aggressively in eastern Manitoba and reproduces rapidly.
- Experts recommend integrated weed management strategies including crop rotation and cover crops.
- Producers are advised against cutting weed control costs too aggressively.
A cool and late spring in Manitoba has delayed weed emergence, creating challenges for farmers and complicating weed management decisions. Weed experts are particularly concerned about herbicide-resistant weeds, including kochia, wild oats, downy brome, waterhemp, and Canada fleabane. Kim Brown, a weed specialist with Manitoba Agriculture, identified these as significant threats. Waterhemp is noted for its aggressive reproduction and has a growing presence in eastern Manitoba, capable of setting seed even after harvest. Kochia resistance is also expanding across the Prairies, with reports of it appearing farther north in Manitoba. Research indicates that a significant portion of tested kochia is resistant to multiple herbicide groups, including Group 14, and some resistance to Group 4 has been detected. Additionally, an increase in kochia 'escapes' when treated with glufosinate has been observed, potentially linked to Group 10 resistance found in waterhemp in the U.S. Midwest. Experts emphasize that new herbicide products often lack novel chemistry, necessitating a broader approach to weed management. Strategies such as enhancing crop competition, implementing crop rotation, adjusting row spacing, ensuring equipment sanitation, and utilizing cover crops are recommended to slow resistance development and reduce weed pressure. Producers are advised against making drastic cuts to weed control budgets, as this could lead to greater future costs. While weed emergence has been slow, some weeds like volunteer canola, lamb's quarters, and dandelions have started appearing. Cool conditions are also slowing crop development. Anne Kirk, a cereal specialist with Manitoba Agriculture, noted that seed treatments can offer valuable insurance during cold springs as crops may remain in the ground longer before emerging.