12 WEED CONTROL IScritical for high yields every year, and for the 2023 growing season, here is the latest advice on several problem species from Mike Cowbrough, weed specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs. He recently presented on this topic at the Ontario Agricultural Conference in early January held at the University of Guelph Ridgetown Campus. Cowbrough focussed on three problem weeds, but before he talked about how best to manage them, he noted that farmers might want to be aware that there may be potential markets for two of them in the years to come. Perennial sow thistle is already a popular medicinal plant in places like Indonesia. It contains cytotoxic steroids that can be used to treat certain cancers. It may also improve exercise performance and alleviate fatigue, and it could be used to treat diabetes and high blood pressure. Field horsetail is being examined as a treatment for arthritis, baldness, and cancer. SOW THISTLE Because sow thistle propagates through seed production and rhizome surface spread, it is critical to address both. Unfortunately, this takes considerable effort. The ability of this weed to quickly enlarge its root mass is impressive. Weed control TIPS FOR THE 2023 GROWING SEASON Treena Hein PERENNIAL SOW THISTLE. PHOTO COURTESY OF MIKE COWBROUGH. Reducing shoot growth is best done in the spring through herbicide use, flaming or cutting, and the key is repetition — stopping re-growth is absolutely critical. In the spring, as with any perennial plant or tree, energy (carbohydrates) is moving from the roots of the sow thistle upward to support shoot growth, and Cowbrough notes that the more shoot growth is stopped, the more the roots will be drained of energy and become smaller — and the likelier it is that the plant will eventually die off. However, there is a trick that Cowbrough shares in terms of the timing of herbicide application. Agronomy
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