ONTARIO GRAIN FARMER 19 AGRONOMY their weed management strategies. By controlling weeds before they emerge, growers can reduce early-season competition. He explains that reducing the number and size of weeds at the time of post-emergence herbicide application makes successful control more likely, while preventing herbicide-resistant weeds from surviving long enough to produce seed. That helps limit the number of resistant weed seeds entering the soil seed bank and reduces pressure for future growing seasons. As resistance concerns grow, more farmers in his area are incorporating preemergence applications into their weed control programs and seeing strong results. Mechanical approaches can also play an important role. Harvest weed seed control, or HWSC, which targets in-season weed seeds before they are returned to the field, has been widely adopted in Australia for more than a decade. The practice has helped reduce resistant weed populations and is often cited as one of the country’s most successful non-chemical resistance management tools. “The challenge is that as soon as you find a strategy that works, you have to think about how to diversify it,” says Flessner. “If growers rely on the same solution year after year, weeds will eventually adapt. Staying ahead of resistance means continually changing the playbook before the weeds do.” AUSTRALIA’S HWSC EXPERIENCE Trevor Thiessen, president of Redekop, based in Saskatoon, works with growers around the world to integrate HWSC technology into their operations using the company’s Seed Control Unit. The system uses mechanical mills mounted on combines to destroy weed seeds at harvest, preventing them from being returned to the field and the soil seed bank. According to Thiessen, the roots of HWSC trace back to Australia’s battle with herbicide-resistant annual ryegrass. By the early 2000s, many growers had exhausted their herbicide options and were searching for alternative ways to manage the weed. Some fed the weeds to sheep, while others baled and removed weed-infested residue from their farms. Despite these efforts, ryegrass continued to spread. A major breakthrough came with the introduction and commercialization of integrated mechanical seed destruction systems in the mid-2010s. Early adopters began seeing significant reductions in ryegrass populations, and the technology quickly gained traction. In regions hardest hit by herbicide-resistant ryegrass, Thiessen estimates mechanical mills were eventually installed on 50 to 80 per cent of combines. “It’s not an immediate fix,” he says, noting that some weed seeds can remain viable in the soil for years. “But research has shown that after three to four years of using a mechanical mill, growers can achieve substantial reductions in weed populations.” While herbicide-resistant annual ryegrass remains a challenge in some parts of Australia, many growers have made significant progress by adopting a diversified approach to weed management. They learned they could not rely solely on herbicides, and have integrated multiple tactics, including HWSC, agronomic strategies, and chemical controls, to reduce weed pressure and slow the spread of resistance. As a result, HWSC remains widely used across Australian crop production regions because growers have learned a hard lesson: once resistant weeds become established, the cost of regaining control can be substantial. “Growers understand that the added cost of running a mechanical mill on the combine is small compared with the cost of losing effective control of resistant weeds,” he says. Thiessen is quick to emphasize that there is no single solution to preventing or managing herbicide resistance, only a combination of tools that can work together over time. Harvest weed seed control is one tool that targets weed seeds during harvest and destroys them before they become a future problem. By reducing the number of viable seeds available for the following season, it helps lower weed pressure in the next crop and can improve the effectiveness of herbicide applications by reducing overall reliance on chemical control. continued on page 20
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