Resistance Management

Prepared by Martha M. Sylvia and Katherine M. Ghantous

Pesticide resistance is an inheritable (genetic) characteristic of a pest that makes it less sensitive to a pesticide and can occur in all types of pests (weeds, insects, fungi, etc.).  Repeated use of the same pesticide (or pesticides with the same mode of action) over time kills pests that are susceptible to the pesticide and leaves behind individuals that are less sensitive.  These then reproduce and pass on the genes that let them survive pesticide exposure to their offspring. The goal in resistance management is to not repeatedly use compounds that fall within the same group.  Resistance management may include alternating products with different modes of action or limiting the total number of applications per season.

International groups have been founded to foster a cooperative approach to resistance management.  They have assigned group numbers to pesticides to help growers make decisions on how to rotate pesticides. They are based on mode of action – how and where the chemicals in the pesticide work on the target.  

In an effort to manage resistance with our pesticides, most labels now come with a “group” number assigned to them.  The group number is specific for each type of pesticide (e.g., Group 1 insecticides have no relation to Group 1 herbicides).  The following 3 pages show the groupings for our cranberry pesticides.  Some active ingredients are available under several different product names, and different active ingredients have the same mode of action. When rotating pesticides for resistance management, use the group number as your guide and NOT the product name or active ingredient.  

The group number is located on the first page of the label, and is usually displayed similarly to this example:

Insecticide Resistance Action Committee (IRAC) 
The Insecticide Resistance Action Committee (IRAC) has been formed to assemble the information for insecticides.  For cranberry, organophosphates and neonicotinoids have the most compounds within their group. We are reliant on several compounds in these groupings.  As long as growers remember to alternate between groupings and not repeat same mode-of-action compounds over and over, we should be able to keep newer compounds viable for decades.  See Cranberry Insecticides by grouping on the next page.  

Fungicide Resistance Action Committee (FRAC)
The group that advises for fungicide resistance is the Fungicide Resistance Action Committee (FRAC).  Their goal is to prolong the effectiveness of fungicides that are likely to encounter resistance problems. For cranberry, Ridomil and Abound are fungicides that are at high risk for resistance development, while Indar and Proline are at medium risk.  They should not be used repeatedly and should be carefully alternated with other fungicides from other groupings.  See Cranberry Fungicides by grouping on following pages.  

Herbicide Resistance Action Committee (HRAC)
The Herbicide Resistance Action Committee and The Weed Science Society of America (WSSA) have developed a classification systems of herbicides.  Previously the WSSA used numbers while HRAC used letters to designate the categories.  As of March 2020, these two systems have been integrated and use numbers to represent groups by mode of action.  One of the purposes of these classification systems is to make it easier for farmers and farm advisors to understand which herbicides share the same mode of action without having to actually know the biochemical basis.  

A key step in resistance management is to minimize the continuous use of herbicides with the same mode of action through rotations and combinations of products. In cranberry, our biggest concern for developing resistance is our reliance on Callisto.  Clethodim and other grass herbicides are also at risk.  Be sure to rotate other compounds into your herbicide schedule.  Do not treat the same bog with Callisto and/or clethodim year after year.    See Cranberry Herbicides by grouping below.