Resistance Debate: Mixtures Or Rotations?

Resistance Debate: Mixtures Or Rotations?

Herbicide rotation is now the most common form of herbicide resistance management practice among growers in Canada. Although herbicide mixture is common, there are obstacles to its becoming as common as rotation. The authors of a new report in Weed Technology conducted a four-year study to determine which method more readily slows herbicide resistance evolution.


From 2004 to 2007, two sites of field pennycress co-occurring with wheat in Saskatchewan were treated with an acetolactate synthase (ALS) inhibitor and bromoxynil/MCPA. Treatments consisted of either a mixture of the two compounds or a rotation of them. For the rotation treatment, by the end of four years the level of resistance of recruited seedlings had increased from 29 percent to 85 percent. For the mixture treatment, by the end of four years the level of resistance was similar to that of the nontreated control.

The authors hope that the findings in this study will encourage the herbicide industry to research and develop a broader range of herbicide mixtures to support what grower surveys and modeling simulations already indicate: mixtures are the superior method for slowing evolution of resistance to herbicides.

To read the entire study, “Selecting for Weed Resistance: Herbicide Rotation and Mixture,” visit