Top 10 Strategies for Managing Herbicide Resistance

Top 10 Strategies for Managing Herbicide Resistance

Two Canadian weed scientists recently published a paper ranking their top 10 herbicide-resistant weed management strategies, and other than one which deals with wheat, all of the tactics are appropriate for Iowa, according to an Iowa State University weed scientist.

Dr. Bob Hartzler, a professor of agronomy and an extension weed specialist at ISU, said in a blog recently that aside from one strategy which deals with the selectivity mechanisms of herbicides used in wheat production, all of the tactics recommended for the Canadian Great Plains are appropriate for Iowa’s production system. One could argue over the ranking of the different strategies, but the critical point is to incorporate as many of the techniques as feasible, he said. 

The ISU Crops Team has emphasized the need for diversifying weed management, with a focus on using multiple, effective herbicide groups, Hartzler wrote. If used alone, multiple herbicide groups will not prevent further evolution of resistance, he said. However, this tactic is easily implemented on all acres. 

"We have focused on this tactic since many...commonly used herbicide programs fail to use herbicides in a way that places significant selection pressure on weeds of concern. Programs often use reduced rates due to economic concerns, thus eliminating much of the benefit of multiple herbicide groups in reducing selection of resistant weeds," according to Hartzler.

The Canadians' number one tactic, crop diversity, is the most effective tool for slowing herbicide resistance. As in the U.S. Cornbelt, the majority of farmers in the Canada prairies utilize a rotation (canola – spring wheat) that provides marginal benefits in terms of managing weeds and herbicide resistance. The authors recognized the economic factors that lead to adoption of crop rotations that contribute to weed resistance. Since most growers are unable or unwilling to adopt the most effective strategy for managing herbicide resistance, Hartzler said it is imperative that the other tactics are utilized.

The following is paraphrasing of their list:

  • Crop diversity;
  • Enhanced competitiveness of the crop;
  • Scouting fields before and after herbicide applications;
  • Multiple herbicide groups;
  • Herbicide group rotation (site of action);
  • Rotation of herbicide selectivity mechanisms in wheat;
  • Weed sanitation;
  • Site-specific weed management;
  • Strategic tillage; and,
  • Accurate recordkeeping.

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