“Start clean and stay clean,” Shaw said.

Rotating herbicide chemistry, including switching mode of action not just products, will reduce potential for resistant weeds to take over. “Also limit the number of applications for any mode of action in any one year.

“Using more than one herbicide chemistry in a given year is an extremely important practice in managing weed resistance,” Shaw said. “That may cost a little more than relying on only one product, but you get enough of a yield bump to get to break even. From a net return standpoint, a pro-active approach is better. Reactive tactics will be more costly.”

Shaw said herbicide mixtures help with resistance management. “Both chemistries must have a high level of activity on target weeds and they must have different modes of action,” he said. “Also, monitor fields within, and across years carefully.”

He said farmers should watch for weeds that are more difficult to control than usual or are of a species known to be resistant in other locations, even in other states.