RM Modes of Action

Modes of Action and Resistance Management

May 15, 2015

This is part of a series of articles on resistance management in crop production. See more resources at cropwatch.unl.edu/resistance-management.

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A key recommendation for resistance management is to not repeatedly use pesticides with the same mode of action. Even if you are using different pesticide active ingredients, repeated use of pesticides with the same mode of action may select for pests able to overcome that pesticide group.

What is a mode of action?  Basically it is how the pesticide kills a pest. For example organophosphate and carbamate insecticides have similar modes of action as Acetylcholinesterase inhibitors. They inhibit an important enzyme responsible for breaking down the chemical acetylcholine, involved in signal transmission in insect and vertebrate nervous systems. Insecticide modes of action are classified using a combination of a number and a letter. For example organophosphate insecticides are classed as group 1B and carbamate insecticides are classed as group 1A.

Where can you find information on pesticide modes of action?  Mode of action classification is done by several industry groups composed of representatives of the companies who register various pesticides with EPA and similar agencies in other countries. For insecticides, this group is the Insecticide Resistance Action Committee (IRAC).  Similar committees exist for Fungicides (FRAC) and Herbicides (HRAC).  Each group has websites where they publish their classification systems, and include educational resources to better understand pesticide modes of action.  In many cases mode of action information is also  provided on pesticide labels.

More Information

Bob Wright
Extension Entomologist