Grainswest - Fall 2025

Fall 2025 grainswest.com 41 “Thanks to recent dry weather patterns kochia is taking over everywhere. We need to find new ways to stop the spread.” —Lewis Baarda ability to thrive in drought conditions has added urgency to the project. “Thanks to recent dry weather patterns kochia is taking over everywhere. We need to find new ways to stop the spread,” said Baarda. “We can’t rely solely on herbicides to manage these weeds in low-lying saline areas, so we’re looking into alternative strategies.” FIELD-TESTED SOLUTIONS Four field locations have been set up within a 150-kilometre radius of Lethbridge to test the effectiveness of 10 IWM strategies on kochia patches in unproductive, low-lying and saline areas of commercial fields. Starting in spring 2025, Baarda and his team began a three- year crop rotation of canola, lentils and spring wheat and will evaluate the impact of control mechanisms that include tillage, double seeding rates, chemfallow, mowing and cutting, direct seeding and competitive crops. The impacts of each strategy on kochia density, biomass and seed presence in the soil will be calculated. While yields will be assessed for controls that impact crops, Baarda noted the overall goal is to determine which approach best manages kochia plants and seed propagation. “We are working at the farm level to find practical solutions that can be easily incorporated into any crop and weed management strategy,” said Baarda. He noted the multi-year approach will enable his team to evaluate the immediate and compounding effects of each method. For example, tillage will bury kochia to remove the weed while burying its seeds to reduce germination. Baarda will also monitor the long-term effects of each control method on the kochia seed bank. He is confident his team’s research will deliver results. “This research will contribute to on-farm solutions for managing kochia. We’re looking to give farmers new options and tools outside of herbicides to maintain the effectiveness of the chemical tools we have, while identifying weed management options that fit their farms. “Controlling established kochia today will reduce the risk next year. Kochia control is everyone’s responsibility, whether it’s on productive cropland or not.” SMARTER WEED CONTROL Tidemann has taken a fresh approach to management of herbicide-resistant weeds. She proposes the use of early maturing crops in rotation to muscle out weeds before they shed seeds and spread. “There are no silver bullet solutions to managing herbicide- resistant wild oats,” she said. “These weeds adapt to just about anything we throw at them, so we challenge ourselves to think outside of the box and find new ways to layer in IWM control methods.” In Manitoba, a recent survey indicated 100 per cent of wild oat samples were resistant to at least one herbicide mode of action. In Saskatchewan, the number is 77 per cent. What’s more, resistances to multiple herbicide groups, particularly Groups 1 and 2, is increasingly common. Building on her earlier PhD research of harvest weed seed control (HWSC), Tidemann conducted a three-year research study (2016 to 2018) to evaluate the effectiveness of combining HWSC with earlier maturing crops to reduce wild oat populations. “Harvest weed seed control isn’t about controlling weeds this season, it’s about doing what’s best for next season and future crops,” she said. By removing or destroying weed seeds at harvest using HWSC methods, and before they can become established in the weed seed bank, farmers can reduce populations in successive years. Wild oats typically mature ahead of harvest. This enables the weed to spread seeds and populations to multiply. To challenge this pattern, she proposed to leverage early maturing crops to beat wild oats before they go to seed. Using HWSC principles, Tidemann set out to remove the weed seeds during harvest. Previous research has shown, due to greater crop competitiveness, early maturing crops such as winter wheat reduce wild oat populations. Tidemann saw potential to further enhance control with rotational diversity and incorporation of HWSC as complementary strategies. To test her theory, Tidemann conducted field trials in four locations across the Prairies. Three-year crop rotations with early, normal or late-maturing crops, including canola, faba beans, flax and peas as well as spring and winter wheat were implemented. Barley was then seeded across all rotations in the final year. Weed seeds were gathered, with chaff collection used as an HWSC method. While she evaluated the impact of crop rotation, she also studied the effects of swathing and straight cutting on weed seed numbers, crop biomass and the seed bank. FRESH THINKING, NEW TACTICS The study clearly proved a combination of IWM control methods is necessary to manage wild oats. Early maturing crops worked well in combination with HWSC. Wild oat seed bank numbers dropped significantly with early maturing crops. And, when HWSC was introduced,