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IRAC's Insecticide Mode of Action Classification1

Frederick M. Fishel 2

This guide explains the rationale behind the Insecticide Resistance Action Committee's (IRAC) insecticide and acaricide mode of action classification and provides a listing of those insecticide common names with their groupings and primary modes of action for insecticides currently registered in Florida.

What is IRAC?

IRAC has groups formed in several countries, including the United States, Brazil, South Africa, Spain, India, and Australia. The group's purpose is to communicate and educate agricultural producers and crop protection professionals by providing resistance management information. Members of an IRAC group are generally professionals who are actively engaged in the insecticide and acaricide manufacturing industry. Some university researchers also participate.

Resistance to Pesticides

Resistance refers to an inheritable change in the sensitivity of a pest population that is reflected by a repeated product failure to achieve the expected control level when used according to the label recommendation for that pest species. Resistance does not always occur, but it has been documented with insecticides as early as 1914. There are many known instances today where resistance is a problem. Not only has resistance occurred with insecticides, but it has also occurred with other pesticides, such as fungicides, herbicides, and rodenticides. Complicating the understanding and management of resistance is the problem of knowing which type of resistance is present in a given pest population. Some pest populations are known to have cross-resistance. That is, they are not effectively controlled with pesticides having the same mode of action that generally targets the same site within the pest. For example, both the carbamate and organophosphate insecticides target acetylcholine esterase, although each group of insecticides is chemically different from one another. The greatest resistance concern arises when multiple-resistance is confirmed. Multiple-resistance is the situation of a pest population that is resistant to pesticides having different modes of action. It is the most difficult type of resistance to manage because the number of management options is reduced. For more information on resistance, see UF/IFAS EDIS Document ENY-624, 2014 Florida Citrus Pest Management Guide: Pesticide Resistance and Resistance Management, https://edis.ifas.ufl.edu/cg026.

IRAC's Classification Scheme

IRAC's insecticide classification scheme is based on mode of action. The goal of the scheme is to provide information to applicators of acaricides and insecticides so they can make sound decisions on selecting insecticides to prevent or manage resistance. Besides selecting products that have different modes of action, growers are also encouraged to integrate other methods into insect and mite control programs. Table 1 contains those acaricides and insecticides registered for use in Florida, though it changes constantly. They are listed according to IRAC's classification scheme by their group and subgroup codes, primary target site of action, chemical sub-group or exemplifying active ingredient, and active ingredient, based on that appearing in version 8.2, 2017, prepared by the IRAC International MoA Working Group.

Using the IRAC Classification Scheme with Product Labels

IRAC is currently encouraging manufacturers of pesticides to indicate the IRAC mode of action group number and description on their product labels; some registrants are now doing so, especially with newer products. Such information would be helpful in assisting pesticide applicators in the selection of acaricides and insecticides for use in resistance management strategies. See Figure 1 for an example of the manner that IRAC is encouraging registrants to list this information.

Figure 1. 
Figure 1. 

Additional Information

IRAC: http://www.irac-online.org/groups/guide/

Rogers, M.E., and M. M. Dewdney. 2016. Florida Citrus Pest Management Guide: Pesticide Resistance and Resistance Management. Gainesville: University of Florida Institute of Food and Agricultural Sciences. https://edis.ifas.ufl.edu/cg026.

Tables

Table 1. 

IRAC's classification scheme for acaricides and insecticides registered for use in Florida.

Footnotes

1. This document is PI-83, one of a series of the Agronomy Department, UF/IFAS Extension. Original publication date October 2005. Revised December 2008, April 2011, April 2014, and March 2017. Reviewed April 2020. Visit the EDIS website at https://edis.ifas.ufl.edu.
2. Frederick M. Fishel, professor, Agronomy Department, and director, Pesticide Information Office; UF/IFAS Extension, Gainesville, FL 32611.

The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication do not signify our approval to the exclusion of other products of suitable composition. Use pesticides safely. Read and follow directions on the manufacturer's label.

Publication #PI-83

Date: 9/20/2020

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