40 The Business of Ontario Agriculture Better Farming | January 2025 crops: the lynch fileS EFFECTIVE WEED CONTROL IN 2024 Timely applications & new tech drive weed control success. By Patrick Lynch For the most part, there was good weed control in fields in 2024. How did this happen? Planting was delayed, so that meant pre-emerge herbicide applications were delayed. The later you spray a pre-emerge herbicide, the later it will be active in the soil. (Before you get the wrong impression, I still believe you should plant as early as possible, and get your pre-emerge herbicide on early, and be ready to spray before emergence.) So, we got pre-emerge herbicides on, and then we had enough rain to activate the herbicides. This resulted in the early flush of weeds being controlled. Then, I believe more growers were scouting their soybean fields than in other years, or had someone scouting them to spray the first flush. I really think that the introduction of waterhemp and Palmer amaranth into Ontario meant more people were checking fields for these new weeds. This resulted in timely respraying of weeds post-emergent. I’ve been asked why we’re getting these new weeds like Canada fleabane, waterhemp and Palmer amaranth. The short answer is: Continuous use of the same group of herbicides. The first resistant weed in Ontario was wild carrot that was resistant to 2,4-D because of its repeated use, mainly by township weed control folks. They really were not aware of what could happen. Then we had triazine-resistant lambsquarters because of overuse of atrazine. We were growing continuous corn using a lot of atrazine. When it no longer controlled certain weeds, we increased the rate and added surfactants and oils. Pretty good recipe to develop resistance. Jump to the 1980s, when a new group of herbicides emerged. They were Group 2, and guess what – Group 2-resistant weeds occurred. I was part of that problem, as I was recommending Clean Sweep, Pursuit (Group 2) and Basagran on soybeans, and Ultim (Group 2) on corn. Sprayer technology has made it easier to touch up weed control and spray nuisance patches of weeds. Becky Howe photo
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