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Proper management techniques are key to catching and containing herbicide resistance to weeds that affect wheat, according to Dallas Peterson, Kansas State University professor of agronomy and Extension weed specialist. “We have to adapt our weed control program over time to adjust to changing conditions,” he said. Peterson spoke about problem weeds and herbicide resistance at the 2009 Bayer Profit Maximizer Wheat Summit sponsored by Bayer CropScience, High Plains Journal and KFRM . Producers must remember that an integrated systems approach is the best way of managing problematic weeds, Peterson explained. “That includes crop rotation, mixing and rotating herbicide modes of action, and timely application of treatments,” he said. “Crop rotation is one of the most powerful tools farmers have,” he added. For example, marestail or horseweed is becoming especially problematic with the shift to no-till production with cotton; but atrazine can effectively control it in corn and sorghum fields, he said. Wheat could be a solution to controlling the weed so that it isn’t as big of an issue in row crops. Relying on only one herbicide to give total control is not advised. Neither is trying to cheat on application rates or timing. “Don’t skimp on the rate or the appropriate spray adjuvants,” Peterson said. “Use appropriate treatments at the appropriate time.” Peterson discussed problematic weeds in wheat such as: winter annual grasses, ALS-resistant weeds, and others, such as wild buckwheat, henbit and marestail. Winter annual grasses are mostly an issue in continuous wheat and wheatfallow- wheat cropping systems, Peterson said. “These are best managed through crop rotation and preventing seed production during the rotational years,” he explained. There have been incidences of ALS-resistant cheatgrass reported in Kansas, he added. “It’s only a matter of time for resistance, and we’re starting to see several cases of poor control with Olympus and Maverick herbicides,” Peterson said. The cases were reported in Cowley and Dickinson counties, and greenhouse experiments confirmed the resistance. Returning to good cultural practices to control these weeds can help producers, Peterson added. Broadleaf weed problems in wheat vary by geography, Peterson said. Mustards are common across the state; henbit and wild buckwheat in eastern and central Kansas; and kochia and Russian thistle westward, he said. ALS-resistant bushy wallflower and flixweed have been reported in the state. Alternative control measures include using 2,4-D, MCPA, or Huskie to achieve acceptable control, Peterson said. Using an integrated systems approach, overall, will help producers identify problem weeds, and control them, for a better bottom line, Peterson explained.
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