Fungicide resistance has been increasing in severity and now is found in many registered products. Resistance is defined as an inherited change in pathogen’s susceptibility to a fungicide. The Environmental Protection Agency (EPA) has developed a voluntary pesticide labeling proposal that groups pesticides with similar modes of action and designates them with a number. The information for fungicides can be found at the Fungicide Resistance Action Committee website at http://www.frac.info/frac/index.htm.

The genetic alterations that create resistant populations occur most rapidly when growers repeatedly apply pesticides with similar modes of action in consecutive sprays. Therefore, it is essential to not spray the same product or similar products against the same target pest in consecutive applications. Single-site fungicides are more likely to develop resistance by pest populations. Recommended product use for single-site fungicides (including many of the new, reduced-risk products) are to completely avoid consecutive sprays. This rule applies when premix products which include a single-site material are used, or if the applications are tank-mixed with single-site products.