FRAC codes help in fungicide resistance management

Rotating fungicides with different FRAC codes can help delay plant pathogen resistance to fungicides, keeping effective products in your disease management toolbox. Attend the 2013 IPM Academy for more details.

Code numbers on fungicide labels, called “FRAC” groups, can help you develop chemical rotations that delay fungicide-resistance in vegetable diseases. Fungicide resistance occurs when repeated applications of a related class of fungicides kill susceptible strains, selectively allowing the survival and reproduction of resistant ones. The ultimate result is that a formerly effective product may no longer work, which is a major problem given the ability of diseases such as Phytophora and powdery mildew to devastate Michigan vegetables.

FRAC code
FRAC codes typically appear in a text box on the upper right corner of the first page of fungicide labels.

Rotation of fungicides with different modes of action is a key component of resistance management and can help maintain good products in your chemical toolbox. However, it is not enough to simply use products with different active ingredients as they could still be related and have the same mode of action. For example, Cabrio and Quadris contain different active ingredients – pyraclostrobin and azoxystrobin, respectively – yet both are in the strobilurin family and attack fungi by the same mechanism.

For this reason, the Fungicide Resistance Action Committee (FRAC) developed a numerical coding system to help you identify products that attack fungi in distinctly different ways. (A similar system has been developed for insecticides.) Simply put, products assigned the same number act the same way, while products that do not share the same numerical group act differently. For example, Cabrio and Quadris are both in FRAC group 11 and reduce the ability of fungi to convert food to energy. However, Folicur, with FRAC-code of 3, acts differently; it is a DMI-fungicide that inhibits production of a critical building block of fungal cell membranes. Rotating among fungicides with different FRAC numbers will help delay development of resistance to any one mode of action.

How can you apply FRAC codes in planning your own fungicide rotation? First, be sure to determine which fungicides provide good control of diseases in your vegetable crop. Michigan State University vegetable specialists, extension educators and crop consultants can help you accomplish this. Next, obtain and read labels for each fungicide and locate their FRAC codes, which are typically on the upper right portion of the first page.

Finally, plan to alternate effective fungicides with different FRAC code numbers to control problem diseases. This will mean you have to incur the additional expense of buying different products. However, in the long run, it will add years to the lives of these chemicals. For this reason, MSU vegetable researchers now make it standard practice to recommend rotation of chemicals for disease control on your farm and often report FRAC codes whenever discussing fungicide trials.

For more information about resistance management and vegetable IPM, register for the upcoming Michigan State University Extension Integrated Pest Management Academy on Feb. 19-20 in Okemos, Mich. The cost of this 2-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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