Understanding FRAC Codes is Important for Managing Fungicide Resistance Development

Andy Wyenandt, Assistant Extension Specialist in Vegetable Pathology, Rutgers University; wyenandt@aesop.rutgers.edu

FRAC, or the Fungicide Resistance Action Committee, was developed to help provide resistance management guidelines for fungicide use. Remember, high-risk fungicides have a high probability of resistance development because of their modes-of-action (MOA). Those fungicides with chemistries that have a specific target site against fungal pathogens, unfortunately, will have a high risk for losing efficacy because of resistance development in the pathogen. Importantly, fungicides with similar chemistries and MOAs that belong to the same FRAC code may also be prone to cross-resistance, where a fungus that develops resistance to one fungicide in the FRAC group may also develop resistance to other fungicides in the group, even if those other fungicides haven’t been used.

With the recent influx of new fungicide chemistries on the market great lengths have been taken to reduce the risk of fungicide resistance development for many fungi where ‘high risk’ fungicides are used. There are currently 43 numbered FRAC groupings and 4 lettered groups. As new fungicides with new MOAs are released on the market, new numbered groups will be added to the list. For many vegetable crops many of the most common fungicides used fall into a few of these groupings, most notably:

Multi-Sites (M) or Low Risk FRAC Groups
M1 and M2, inorganics such as sulfur and copper
M3, Maneb or Mancozeb
M5, chlorothalonil such as Bravo

Higher Risk FRAC Groups
Group 3, triazoles such as Nova or Rally
Group 4, mefenoxams such as Ridomil
Group 11, strobilurins such as Quardris, Flint, Cabrio

Some of the newest fungicides labeled for use in vegetable production include Quintec (quinoxyfen, FRAC code 13) and Revus (mandipropamid, 40).

Knowing which fungicides belong to which FRAC code will have an impact on spray schedules, disease control, and resistance management. Protectant fungicides, such as those in the FRAC code M, have a low risk for fungicide resistance development and have less stringent restrictions. However, for those chemicals with a higher risk of fungicide resistance development the product labels are more stringent and labels should be followed precisely. Labels often require that high-risk fungicides be tank-mixed with protectant fungicides to reduce the chances for fungicide resistance development. In general, tank mixing high-risk fungicides with protectant fungicides is always a good resistance management strategy. For example and, in general, the strobilurin fungicides in FRAC code 11 should not be sprayed consecutively. Such that, if Quadris (azoxystrobin, 11) is sprayed one week, it should not be followed the next week with another Group 11 compound such as Flint (trifloxystrobin, 11) or Cabrio (pyraclostrobin, 11) or a compound containing a Group 11 fungicide (Pristine, pyraclostrobin + boscalid, 11 + 7). A simple way to remember what to use next in your fungicide rotation is to use a labeled fungicide with a different FRAC number or letter. FRAC codes can be found in the fungicide table at the beginning of each crop section in the 2008 Commercial Vegetable Production Recommendations to help growers learn what fungicides belong to what FRAC groups and to help them chose fungicides for use in rotations. A complete list of fungicides and FRAC groups can also be found in Table E-8 on pages E30 and E31 in the Vegetable Production Recommendations. Efforts in learning and using new chemistries with new modes of action along with knowing their FRAC grouping will ultimately pay off in the long run by reducing the chances for fungicide resistance development.

Delaware Growers – Fungicide Resistance Management Guidelines for Vegetables were distributed at Ag Week with the Vegetable Production Recommendations. If you did not receive one and would like a copy, request one from the county Extension office or stop by and pick one up. These guides were developed as a project directed by Andy Wyenandt at Rutgers assisted by the other plant pathologists in the mid-Atlantic region and funded in part by the Northeastern IPM Center and USDA/CSREES.

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