IRAC codes help in insecticide resistance management

Check IRAC codes to help with rotating insecticides to delay insect pest resistance and maintain the availability of key products. Attend the 2013 IPM Academy for more details.

Codes on insecticide labels, called “IRAC” codes, can help you develop chemical rotations that delay insecticide resistance in populations of insect pests that attack vegetables. Insecticide resistance occurs when repeated applications of a related class of compounds kill susceptible insects, selectively allowing the survival and reproduction of resistant individuals. Over time, this will increase the percentage of insects in a pest population that are resistant, so that a formerly effective product no longer works. 

IRAC code
On newer insecticide labels, IRAC codes appear in a text box on the upper right corner of the first page.

For example, azinphos-methyl (Guthion), once effective against Colorado potato beetle, now provides only limited control of resistant populations in Michigan. (For more information on pesticide resistance for different pest species, visit the Arthropod Pesticide Resistance Database; you will need to know the genus and species of a pest to query the resistance database.) One strategy used to reduce resistance is to rotate insecticides with different modes of action.

To enable you to do this effectively, the Insecticide Resistance Action Committee (IRAC) developed a numerical coding system to help you identify products that attack insect pests in different ways. (Note, similar codes called “FRAC” codes have been developed for fungicides.) Simply put, products assigned the same number have the same mode of action, while products that do not share the same numerical code act differently. For example, Radiant and SpinTor are both Group 5 insecticides and target receptors in insect nerve cells. In contrast, Ambush and Warrior are both Group 3 insecticides and act on the sodium channels of insect nerve cells.

When possible, plan to target different generations of a pest species with a rotation of products that have different IRAC numbers. For pests that have multiple generations in a single season, such as onion thrips, this will mean rotating products with different IRAC numbers within a single growing season. For pests with only a single generation per year, such as Japanese beetles, rotate products from year to year.

To locate a product’s IRAC code, search for the “Insecticide Resistance Management” portion of the label. This section typically contains the IRAC number in a statement such as “this product is a Group 5 insecticide.” Many newer labels also display IRAC numbers on the upper right corner of the front page.

If a label does not have an IRAC code, you can contact a local Michigan State University Extension educator or visit the IRAC database. You will need to know the product’s active ingredient to query the database; see information on how to read a pesticide label). MSU Extension educators can also help you consider the many other facets of effective insecticide use.

For more information about resistance management and integrated pest management in general, register for the upcoming Michigan State University Extension Integrated Pest Management Academy on Feb. 19-20 in Okemos, Mich. The cost of this two-day program is $225. Registration is open through Feb. 12, but space is limited so register today. For more information, or to request a paper registration form, please contact Erin Lizotte at 231-944-6504.

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