8 In addition, weeds like Canada fleabane are easy to control in the fall but display variable control in the spring. Higher yields are also a result of fall herbicide application, says Ferrier. "We know that fall weed interference pulls yield from fall-seeded crops. In four winter wheat trials in 2020-2021, our Nufarm research program showed an average of 12 bu/ac gained by implementing a fall herbicide program over not spraying. I know that most growers would have still sprayed inthe spring, but this demonstrates the magnitude of yield loss due to weeds in winter wheat." He adds that researchers like Dr. Eric Johnson have demonstrated that a fall herbicide application containing pyroxasulfone (Fierce, Zidua) before planting winter wheat could provide over 80 per cent control of grasses the following season. Cowbrough agrees that a fall or superearly spring application of herbicides effectively controls perennials like bluegrass, rye grass, or brome grass in corn and winter wheat. "Tillage should also be examined as a control method, and again, cover crops," he says. "This problem is coming from tight rotations, and we're seeing more of it, and I feel like in some areas we're at a tipping point. Please consider fall herbicide, tillage and seed cover crops." FOR MORE Find out more, including a common ragweed resistance map along with details for resistance testing and an overview of integrated pest management strategies, which Cowbrough notes apply to most weeds at https://fieldcropnews.com/2017/10/commonragweed-biology-and-control/. l WHEAT FIELD UNTREATED. PHOTO COURTESY OF JAMES FERRIER, NUFARM. continued from page 6 riskier to get establishment after grain corn, so try it on a small scale, experiment with it and scale it up. Besides weed suppression, it also reduces erosion. And when conditions after herbicide application are dry, and the risk of herbicide carryover is greater, cover crops can help alleviate the risk to some extent." FALL APPLICATION Ferrier notes that while some farmers have been doing fall or post-harvest burndown herbicide application after winter wheat or soybean harvest for many years, new research showing its value may prompt more to try it. "The goal is to target weeds that emerged late in the current crop and to clean up the field for planting fall cereal crops," he says. "Weeds are easiest to control when small and actively growing, and many perennial and winter annual weeds are smallest and easiest to control in the fall."
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