Fungicides have been divided into many FRAC groups based upon their mode of action, but not all of these groups are used in the Turf industry. The key FRAC groups of interest to golf course superintendents and other turf managers include: M2 – Dithiocarbamates, M4 – Nitriles, 1 - Benzimidazoles , 2 – Dicarboximides, 3 - Demethylation Inhibitors (DMI), 4 – Phenylamides, 7 - Carboximides, 11 – Strobilurins (QoI), 12 - Phenylpyrrole , 14 - Aromatic hydrocarbons, 19 – Polyoxins, 28 – Carbamate, 33 - Phosphonates, and Miscellaneous. A brief description of these groups follows:
Contact Groups include 12, 14, and the M’s. Groups with an M in their classification are products with a multiple site mode of action and function as protectants. M2 – Dithiocarbamates include mancozeb (Protect) with an enzyme inactivation mode of action, thiram (Spotrete F, Defiant WDG) which chelates metal ions allowing them to pass through fungal cells. Chlorothalonil (Daconil) is the chemistry in the M4 - Phenylamides and causes cell membrane toxicity. Fludioxil (Medallion) falls into FRAC 12 - Phenylpyrrole and functions by causing cell lysis and inhibiting amino acid uptake. The fourth group within the contact/protectant cassification is FRAC 14 - Aromatic hydrocarbons. Active ingredients within this group include chloroneb (Terremec SP), ethazole (Terrazole), and quintozene (Terrachlor, PCNB). The aromatic hydrocarbons achieve control by interfering with mitosis. There is low risk of resistance for the contact/protectant products that we use in the turfgrass industry and cross resistance is not expected. Because these products are contacts they need to be applied uniformly to the plant surface being protected. The product should be allowed to dry so that it does not get washed off the leaf surface. Reapplication at the appropriate interval is necessary to protect any plant tissue that has grown since the last application.
The remaining groups hold chemicals that enter the plant, either as penetrants or as systemic. Thiophanate methyl is in the FRAC I – Benzimidazole group and includes the 3336 and 3336 Plus product line. Thiophanate methyl works by binding tubulin subunits resulting in mitotic inhibition. The FRAC 2 – Dicarboximides include iprodione (Chipco 26GT) and vinclozolin (Curalan) and work by affecting DNA synthesis and lipid metabolism. FRAC 3 - Demethylation Inhibitors or DMI’s, for short, are a group of penetrant fungicides. Active ingredients within this group include fenarimol (Rubigan), myclobutanil (Eagle), propiconazole (Banner Maxx), and triadimefon (Bayleton) and work by inhibiting the synthesis of ergosterol in the fungal cell membrane. FRAC 4 - Phenylamides chemistries include mefanoxam (Subdue Maxx) and metalaxyl and work by inhibiting the fungi’s ability to synthesize RNA. Turfgrass chemistries in FRAC 7 – Carboximides include flutolanil (ProStar), oxycarboxin (Arrest), boscalid (Emerald). These chemistries block activity of various respiratory enzymes. FRAC 11 – Strobilurins include azoxystrobin (Heritage), fluoxastrobin (Disarm), pyraclostrobin (Insignia), and triflozystrobin (Compass). These chemistries work by blocking fungi from generating ATP. FRAC 19 – Polyoxins contains polyoxin-D (Endorse). Polyoxin-D is a novel chemistry that inhibits fungal spore germination and inhibits the production of cell wall components (chitin). FRAC – 28 Carbamates include propamocarb hydrochloride (Banol). Propamocarb is a localized penetrant that achieves control by altering cell membrane function. The FRAC 33 - Phosphonates are true systemic fungicides and include fosetyl-Al (Aliette, Chipco Signature) and the phosphites (Alude). These chemistries provide control by inhibiting oxidative phosphorylation in the target pathogen as well as stimulating the plant's natural defense response to pathogen attack. These fungicides should be allowed to enter the plant before any water is applied. Similar to the contact fungicides, at a minimum the spray should be allowed to dry to insure that the chemistry has made its way into the plant.
As new chemistries are developed they are classified as miscellaneous (unknown) until they can be put into one of the existing categories and the risk of resistance is ascertained to assist in their management. Risk of resistance is already a concern in several of the chemistries used today. Fungal pathogens have been shown to develop resistance to the benzimidazoles, carboximides, dicarboximdes, DMI’s, phenylamides, and the strobilurins. Evaluation of current spray programs is important to insure that all of these chemistries will be available in the future. Developing a spray program should be based on several factors, but product mode of action may be the most important. Tank mixes should not contain products with the same FRAC group. Rotation of the mode of action should be practiced to avoid the selection of resistant fungal strains. If you recall the iprodione/vinclozolin example in part one of this article you will remember that cross resistance has already been documented for these active ingredients. Rotating these dicarboximides does not reduce the buildup of resistant strains because they have the same mode of action. Rotating applications based on name brand does absolutely nothing to manage resistance if modes of action are not taken into account.
The next time you take a look at your spray program you should ask yourself these 3 questions:
• How many FRAC groups do I have in my program?
• Have I been rotating these FRAC groups?
• Have I been adding products with the same FRAC group into the tank mixes?
And remember that Cleary has developed the Cleary Technical Information Bulletin “Turf and Ornamental Fungicides Grouped by Mode of Action (MOA)” to assist you in reviewing the products in your spray program and to insure that you are using proper tank mix partners. Cleary also packages products with the FRAC Group displayed on the front of the package so that even if you do not have full detail of the specific MOA of your product you can still decide which combinations to avoid.
© Cleary Chemical 2008