ONTARIO GRAIN FARMER 26 AGRONOMY Similar to Cowbrough’s approach, Sharpe encourages growers to adopt a mix of weed control practices that make practical and economic sense. “Chemicals are still the backbone of how we manage weeds in crop production systems,” notes Sharpe, reminding growers that every field requires its own unique strategy that includes cultural and chemical solutions. “What we need to do is preserve their effectiveness by introducing cultural practices and strategies that complement chemicals to ease the pressure and reliance.” KNOW YOUR PROBLEM WEEDS “The biggest weed problem is the species that’s in your field,” says Cowbrough, reminding growers that any weed can be a problem, even those that aren’t herbicide tolerant. While pigweed species, including red, green, waterhemp, and Palmer amaranth, are among the most concerning herbicide-resistant weeds in Ontario, the most common problem weed is actually lamb’squarters because of its abundance. Bluegrass and herbicide-resistant ryegrass are also on Cowbrough’s radar. Both are perennial species that can be difficult to control, particularly in soybeans and wheat, and have become more persistent over the past five years. He believes bluegrass infestations may be spreading from established populations along roadsides into fields. One of the main weed control challenges is cost, as herbicides targeting these grassy weeds can be more expensive and must be used alongside broadleaf control products. “Not a lot of growers are affected yet, but these grassy weeds are significant and can become a real problem once they are established in a field,” says Cowbrough. continued from page 25 According to Sharpe, kochia remains the dominant problem weed in Western Canada, especially as it continues to spread northward. Palmer amaranth is also on his radar, and he is watching closely as it advances through the U.S. and threatens both Eastern and Western Canada. MANAGING WEEDS Managing herbicide-resistant weeds requires practical strategies, along with a willingness to get creative when necessary. Sharpe says diversification is essential to manage weeds, including herbicides, crop types and rotations, and, “approaches to just about every aspect of crop management.” Cultural practices such as seeding timing, seedbed preparation, planting competitive crops, mowing weed patches, seeding cover crops, and interseeding should all be considered when preventing or dealing with herbicide-resistant weeds. For growers dealing with herbicide-resistant waterhemp or other pigweed species, timing is also critical. These weeds can emerge throughout the growing season and even after harvest, allowing them to establish and gain a head start the following year. “There’s no magical herbicide that gives residual control after harvest,” he points out, but strategic herbicide applications can help extend control. He recommends a two-pass weed control strategy to establish and extend residual activity for as long as possible, reducing the risk of late-season weed escapes. One of the most important aspects of managing herbicide-resistant weeds is proper identification. Cowbrough explains that resistance can be confirmed through two methods: molecular testing and plant bioassay. Both are available to Ontario growers, with testing information and sample collection tips accessible through OMAFA resources. “It’s important to know what species of weed resistance you have in your field in order to prevent it from spreading,” states Cowbrough. Ryegrass Kochia
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