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Publication #PI94

Fungicide Resistance Action Committee's (FRAC) Classification Scheme of Fungicides According to Mode of Action1

F.M. Fishel and M.M. Dewdney2

This guide addresses management of pesticide resistance and describes the Fungicide Resistance Action Committee's (FRAC) classification of fungicides and bactericides registered for agricultural and non-agricultural use in Florida by their modes of action. A cross-reference of common names for active ingredients, along with corresponding examples of their trade names, is also provided.

Fungicide-resistant plant pathogens are not new. Although the first confirmation of fungicide resistance was in 1960, there were few subsequent occurrences until 1970. Since then, fungicide resistance has not been infrequent, especially with the introduction of systemic fungicides. There has been concern that the time it takes for resistance to emerge has been shortening. Sometimes resistance occurs within two years of a new commercial fungicide introduction. The development of rapid resistance is related to the increased specificity of targets and selection pressure on the target population.

Resistance problems are not unique to plant pathogens. Insecticide-resistant insects, herbicide-resistant weeds, and antibiotic-resistant bacteria are well-documented. These resistant pests have two common traits: 1) they have exceptionally large populations and 2) a rapid rate of reproduction. Weeds were the last category of pests to show resistance because there is a very large seed bank in the soil with many individuals that have limited pesticide exposure. In contrast, insects reproduce with multiple generations in a single year, and some bacteria reproduce several times in a single hour. In both cases, there is less of a population reservoir with these organisms.

Where large populations exist, great genetic diversity exists in the population. In these large populations, several individuals will be tolerant of chemical-control measures, perhaps only one in a million or one in a billion. Pests typically become resistant when the same pesticide is used repeatedly within a single year or for several consecutive years. Some individuals believed that selection pressure forced pests to mutate, but this view has been largely discounted through research. However, more accepted reasons for resistance are as follows:

  • There was always a small resistant population present from natural variation.

  • When a pesticide is applied, the susceptible population is controlled, but the smaller, resistant population becomes a larger proportion of the population that re-infests the site.

Cross-Resistance versus Multiple-Resistance

Agricultural producers in Florida have the option of using more than 50 different fungicide active ingredients and many more trade products, including mixtures. Many of these active ingredients work in the same way; in other words, they have the same mode of action. Despite the numerous trade products available, these fungicides affect fewer than 20 growth mechanisms.

A plant pathogen is cross-resistant when it cannot be controlled by fungicides affecting the same growth process. An example of a plant pathogen that has cross-resistance is one resistant to fungicides in the triazoles or pyrimidines chemical groups. Both of these are demethylation inhibitors (DMI) that disrupt sterol synthesis.

A more serious concern is multiple-resistance. This phenomenon occurs when a plant pathogen is not controlled by fungicides that affect different growth processes. For example, if a plant pathogen is resistant to fungicides that inhibit both mitosis and protein synthesis, two different fungal growth processes, it would be labeled as having multiple-resistance.

Fungicide Selection

Farmers and crop advisors need to know which fungicides are best suited to combat resistant plant pathogens. Some manufacturers use the FRAC numerical classification of fungicides (listed in Table 1) to support the use of fungicides in a manner suitable for resistance management. The fungicides are classified according to their modes of action, collective and chemical group names, and active ingredient common names. Some examples of popular trade names are provided in Table 2 as a cross-reference.

The tables only include fungicides available in Florida. Those with an intrinsic “high risk” of resistance selection are identified. “High risk” is determined by the following:

Fungicide Indicators

  • The product activity persists over time, or there is the practice of repetitive use or sustained treatments.

  • There is only one target for the mode of action.

  • Only one gene needs to be mutated for a fungus to be no longer susceptible.

  • The product is easily metabolized by the target fungus.

Pathogen Indicators

  • There is cross-resistance with existing fungicides.

  • There is high genetic variability within the target plant pathogen population.

  • The target plant pathogens are known to have large populations with rapid multiplication.

  • The target plant pathogen multiplies rapidly with frequent generations.

  • Some target organisms possess the ability to metabolize products.

  • There are no harmful effects on resistant individuals.

FRAC encourages fungicide registrants to use this system to indicate the mode-of-action group in a uniform location on their product labels. Some registrants identify the mode-of-action group on the front panel of their product labels.

Similar systems have been proposed and encouraged for herbicides and insecticides.

Agricultural producers can have difficulty keeping track of which modes of action they use because of the great variety of trade names and package mixtures of fungicides.

Additional Information

Fungicide Resistance Action Committee (FRAC). Accessed November 2012. http://www.frac.info/.

OEPP/EPPO. 2002. “EPPO Standard PP 1/213(1) Revision. Resistance Risk Analysis.” Bulletin OEPP/EPPO Bulletin 33:37-63.

Rogers, M.E., and M.M. Dewdney. 2012. 2012 Florida Citrus Pest Management Guide: Pesticide Resistance and Resistance Management. ENY-624. Gainesville, FL: University of Florida Institute of Food and Agricultural Sciences. http://edis.ifas.ufl.edu/cg026.

Tomlin, C.D.S., ed. 2003. The Pesticide Manual: A World Compendium, 13th edition. The British Crop Protection Council.

Tables

Table 1. 

FRAC's classification of fungicides registered for use in Florida by FRAC numerical code, mode of action, target site of action, and active ingredient common name with resistance risk indication.

FRAC code*

Mode of action

Target site of action

Active ingredient common name

Resistance risk

4

Nucleic acid synthesis

RNA polymerase I

Metalaxyl

HIGH

Metalaxyl-M (Mefenoxam)

32

DNA/RNA synthesis (proposed)

Octhilinone

RESISTANCE NOT KNOWN

1

Mitosis and cell division

ß-tubulin assembly in mitosis

Carbendazim

HIGH

Thiabendazole

Thiophanate-methyl

22

Zoxamide

LOW TO MEDIUM

43

Delocalisation of spectrin-like proteins

Fluopicolide

RESISTANCE NOT KNOWN

7

Respiration

Complex II: succinate-dehydrogenase

Flutolanil

MEDIUM TO HIGH

Carboxin

Fluopyram

Boscalid

11

Complex III: cytochrome bc1 (ubiquinol oxidase) at Qo site (cyt b gene)

Azoxystrobin

HIGH

Pyraoxystrobin

Pyraclostrobin

Kresoxim-methyl

Trifloxystrobin

Famoxodone

Fluoxastrobin

Fenamidone

21

Complex III: cytochrome bc1 (ubiquinone reductase) at Qi site

Cyazofamid

RESISTANCE RISK UNKNOWN BUT ASSUMED TO BE MEDIUM TO HIGH

29

Uncouplers of oxidative phosphorylation

Fluazinam

LOW

30

Inhibitors of oxidative phosphorylation, ATP synthase

Fentin hydroxide

LOW TO MEDIUM

9

Amino acids and protein synthesis

Methionine biosynthesis (proposed) (cgs gene)

Cyprodinil

MEDIUM

Pyrimethanil

25

Protein synthesis (bactericides)

Streptomycin

HIGH

41

Oxytetracycline

13

Signal transduction

Mechanism unknown

Quinoxyfen

MEDIUM

12

MAP/Histidine-kinase in osmotic signal transduction (os-2, HOG1)

Fludioxonil

LOW TO MEDIUM

2

MAP/Histidine-kinase in osmotic signal transduction (os-1, Daf1)

Iprodione

MEDIUM TO HIGH

Cross-resistance common

 

Vinclozolin

14

Lipid synthesis and membrane integrity

Lipid peroxidation (proposed)

Chloroneb

LOW TO MEDIUM

Dicloran

Etridiazole

28

Cell membrane permeability, fatty acids (proposed)

Propamocarb

44

Microbial disrupters of pathogen cell membranes

Bacillus subtilis

ASSUMED TO BE LOW

3

Sterol biosynthesis in membranes

C14-demethylase in sterol biosynthesis (erg11/cyp51)

Triforine

MEDIUM

Fernarimol

Imazalil

Triflumizole

Cyproconazole

Difenoconazole

Fenbuconazole

Flutriafol

Ipconazole

Metconazole

Myclobutanil

Propiconazole

Prothioconazole

Tetraconazole

Triadimefon

Triadimenol

Triticonazole

5

 

Δ14-reductase and Δ8→ Δ7-isomerase in sterol biosynthesis (erg24, erg2)

Piperalin

LOW TO MEDIUM

17

 

3-keto reductase, C4-demethylation (erg27)

Fenhexamid

19

Cell wall biosynthesis

Chitin synthase

Polyoxin

MEDIUM

40

Cellulose synthase

Dimethomorph

LOW TO MEDIUM Cross-resistance

Mandipropamid

P

Host plant defense induction

P1: Salicylic acid pathway

Acibenzolar-S-methyl

NOT KNOWN

 

P4 (proposed)

Laminarin

27

Unknown mode of action

Unknown

Cymoxanil

LOW TO MEDIUM

33

Fosetyl-Al

LOW

Phosphorous acid and salts

U12

Cell membrane disruption (proposed)

Dodine

LOW TO MEDIUM

NC

Not classified

Diverse

Mineral oils, organic oils, potassium bicarbonate, material of biological origin

NOT KNOWN

M1

Multi-site contact activity

Multi-site contact activity

Copper (different salts)

LOW

M2

Sulfur

M3

Ferbam

Mancozeb

Maneb

Metiram

Thiram

Ziram

M4

Captan

 

Folpet

M5

Chlorothalonil

*Numbers and letters are used to distinguish the fungicide groups. The numbers were assigned primarily according to the time of product introduction to the market. The letter abbreviations are as follows: P = host plant defense inducers; M = multi-site contact activity; U = unknown mode of action; and, NC = not classified.

Table 2. 

Cross-listing of active ingredient common names with trade products registered for use in Florida.

Common name

Trade products*®

Acibenzolar-S-methyl

Actigard, Blockade

Azoxystrobin (HIGH RISK)

Abound, Amistar, Azo-Shield, Azotech, Cruiser, Dynasty, Graduate A+, Headway, Heritage, Highway, Maxide, Maxim Quattro, Optishield, Quadris, Quadris Top, Quilt, Renown, Seed Shield, Sporgard, Trio Extra, Uniform

Bacillus subtilis

Companion, Histick, Integral, Kodiak, Premiere, Pro-Mix, Subtilex, System 3

Boscalid

Endura, Pristine

Captan

Captan, Captec, Captevate, Enhance, Fungitrol, Hi-Moly, Rescue, SA-50, Trilex, Vitavax PC

Carbendazim (HIGH RISK)

Bioban, Fungiblock, Mauget, Mergal, Polyphase, Rocima, Troysan

Carboxin

Allerax, Cotgard, Enhance, Kernel Guard, Latitude, Prevail, Vitavax

Chloroneb

IX, Teremec, Terramec

Chlorothalonil

Acticide PAX, Aftershock, Antiblu, Applause, Bravo, Busan, Catamaran, Chemtreat, Chloro Gold, Chloronil, Chlorosel, Chlorostar, Chlorothalonil, Chlortram, Cleanwood, CLT, Concert, Concorde, Consyst, Countdown, Daconil, Densil, Disarm, Docket, Echo, Ensign, Equus, Exotherm, Flouronil, Fungitrol, Fungonil, Initiate, Instrata, Legend, Mainsail, Manicure, Maxide, Mold-Ram Nopcocide, Pegasus, Peregrine, Prominence, Quadris, Quali-Pro, Renown, Reserve, Ridomil, Rocima, SA-50, Spectro, Tee-1-Up, Thalonil, Thor, Tilt, TM, Vitalonil

Copper (carbonate)

CMC, Micropro, Phibrowood, Sustain, UCU, Wolman E

Copper (ethanolamine complex)

Various swimming pool treatments

Copper (ethylenediamine complex)

Current, Harpoon, Komeen, Pondmaster

Copper (hydroxide)

Champ, Champion, Cu-Bor, Cupro, Funguran, GX-569, Junction, Kentan, Kocide, Kop-Hydroxide, Mankocide, Neptune, Nu-Cop, Ridomil Gold Copper, Spin Out

Copper (metallic)

Various algaecides and anti-fouling paints

Copper (naphthenate)

Various wood preservatives

Copper (oxychloride)

Agra Cop, Badge, COC

Copper (salts of fatty and rosin acids)

Camelot, Tenn-Cop

Copper (sulfate pentahydrate)

Various swimming pool treatments, Magna-Bon CS 2005, Phyton 27 AG

Copper (triethanolamine complex)

Various algaecides and other water treatments

Copper (I oxide)

Various anti-fouling paints

Copper (II oxide)

Various wood preservatives

Cyazofamid

Ranman, Segway

Cymoxanil

Curzate, Evolve, Tanos

Cyproconazole

Alto, Quadris Xtra

Cyprodinil

Inspire Super, Palladium, Switch, Vangard

Dicloran

Botran

Difenoconazole

Amdro, Cruiser, Dividend, Inspire, Quadris Top, Revus, Seed Shield

Dimethomorph

Acrobat, Forum, Stature

Dodine

Elast

Etridiazole

Banrot, Koban, Terraclor, Terramaster, Terrazole, Truban

Famoxadone (HIGH RISK)

Tanos

Fenamidone (HIGH RISK)

Fenstop, Reason

Fenarimol

Rubigan

Fenbuconazole

Enable, Indar

Fenhexamid

Captevate, Decree, Elevate

Fentin hydroxide

Agri Tin, Enable, Orbit, Super Tin

Ferbam

Ferbam

Fluazinam

Omega

Fludioxonil

Apron, Cannonball, Cruiser, Dynasty, Fludi-Shield, Graduate, Graduate A+, Hurricane, Instrata, Maxim, Medallion, Mozart, Optishield, Palladium, Scholar, Seed Shield, Sporgard, Switch, Trio Extra, Warden

Fluopicolide

Adorn, Presidio, Stellar

Fluopyram

Luna Experience, Luna Sensation, Luna Tranquility

Fluoxastrobin (HIGH RISK)

Aftershock, Disarm, Evito

Flutolanil

Artisan, Contrast, Convoy, Moncoat, Moncut, Prostar, Sysstar

Flutriafol

Topguard

Folpet

Folpet, Fungitrol, several wood preservatives

Fosetyl-Al

Aliette, Armortech, Autograph, Avalon, Flanker, Fosetyl-Al, Gimme, Legion, Linebacker, Novasource, Prodigy Signature, Viceroy

Imazalil

Clinafarm, Deccozil, Freshgard, Fungaflor, Magnate, Pacrite

Ipconazole

Acceleron, Inovate, Rancona, Vortex

Iprodione

26/36, 26GT, Andersons, Armortech, Chipco, Dovetail, Enclosure, Iprodione, Lesco, Nevado, OHP, Primeraone, Quali-Pro, Raven, Rovral, Tazz, TM + IP

Kresoxim-methyl (HIGH RISK)

Cygnus, Sovran

Laminarin

Vacciplant

Mancozeb

Acrobat MZ, Clevis, Cuprofix MZ, Dithane, Evolve, Fore, Gaucho, Gavel, Junction, Koverall, Manco-Phite, Mancozeb, Mancozide, Manhandle, Manzate, Maxim, Moncoat, Penncozeb, Pentathlon, Potato Seed Treater, Protect, Ridomil Gold MZ, SA-50, Stature, Tops MZ, Wingman, Zyban

Mandipropamid

Revus

Maneb

Maneb, Manex

Metalaxyl (HIGH RISK)

Acceleron, Acquire, Allegiance, Allerax, Charter, Cotgard, Dyna-Shield, Inovate, Latitude, Metastar, Prevail, Protector, Rancona, Sebring, Spera, Stamina, System 3, Trilex

Metalaxyl-M (Mefenoxam) (HIGH RISK)

Apron, Axle, Cruiser, Dividend, Dynasty, Fenox Flouronil, Hurricane, Maxim, Mefenoxam, Ridomil Gold, Seed Shield, Subdue, Trio Extra, Twist, Ultra Flourish, Uniform, Warden

Metconazole

Caramba, Headline, Metlock, Quash, Tourney, Twinline

Metiram

Cabrio, Polyram

Mineral oils

435, 455, 692, 796, All Seasons, Biocover, Bonide, BVA, Civitas, Damoil, GB-1111, Mite-E-Oil, Omni, Parafine, Pervade, Pest Fighter, Prescription, Purespray, Ready-To-Use, RTSA, SA-50, Sol-Oil, Soluble Oil, Spray Fluid, Stylet Oil, Triangle, Volck, Year-Round

Myclobutanil

Acceleron, Armortech, Disarm, Dynasty, Eagle, F-Stop, Green Light, Greenview, Hoist, Immunox, Laredo, Manhandle, Myclobutanil, Myclotect, Nova, Rally, Siskin, Sonoma, Spera Coat

Octhilinone

Acticide, Arch, Bio/Tec 95, Bioban, Cleanwood, Intercept, Kathon, Moldex, Rocima, Skane, Tex-Stat, Thor, Troysan

Oxytetracycline (HIGH RISK)

Bacastat, Fireline, Mycoject, OTC

Phosphorous acid

Magellan, Phostrol

Piperalin

Pipron

Polyoxin

Affirm, Endorse, Ph-D, Veranda

Potassium bicarbonate

Armicarb, Kaligreen, Milstop

Propamocarb

Banol, Previcur, Promess, Proplant, Stellar

Propiconazole

Alamo, Amtide, Antiblu, Armortech, Artisan, Avaris, Banner, Bumper, Busan, CB-300, Concert, Dorado, Dual Action, Fathom, Fitness, Frameguard, Headway, Highway, Honor Guard, Instrata, Kestrel, Kop-Coat, Monterey, Mycostat, Orbit, Pack PT, Premier, Primeraone, Procon, Prophesy, Propensity, Propiconazole, Propimax, Propi-Star, Prosan, Quilt, Savvi, Shepherd, Solera, Spectator, Star-Shield, Stratego, Strider, Tilt, Troysan, Wocosen, Wolman

Prothioconazole

Proline, Prosaro, Provost, Stratego

Pyraclostrobin (HIGH RISK)

Acceleron, Cabrio, Coronet, Diamir, Headline, Honor, Insignia, Pageant, Pristine, Stamina, Twinline

Pyrimethanil

Distinguish, Freshgard, Luna Tranquility, Pacrite, Penbotec, Philabuster, Scala

Quinoxyfen

Quintec

Streptomycin (HIGH RISK)

Ag Streptomycin, Agri Mycin, Firewall

Sulfur

Many commercial products

Tebuconazole

Absolute, Luna Experience

Tetraconazole

Domark, Mettle

Thiabendazole (HIGH RISK)

Add-2, Alumni, Azotech, Decco Salt, Freshgard, HDH, Krud Kutter, Maxim Quattro, Mertect, Metasol, Optishield, Shield-Brite, Sporgard, Stay-Clean, Tecto

Thiophanate-methyl (HIGH RISK)

26/36, 3336, Allban, Armortech, Banrot, Cavalier, Dovetail, Evolve, Fungo, Infuse, OHP, Peregrine, Primeraone, Prominence, Quali-Pro, Regal Consyst, SA-50, Spectro, Sysstar, Systec, T-Bird, T-Methyl, Tee-1-Up, Tee-Off, Thiophanate-methyl, TM, Tops, Topsin, Transom, T-Storm, Trilex Star

Thiram

42-S, Allerax, Defiant, Flowsan, Raxil, Rootone, Spotrete, Protector L, Thiram, Vitavax

Triadimefon

SA-50, Armada, Bayleton, Fung Away, Fungicide VII, Strike, Tartan, Turf

Triadimenol

Trilex

Trifloxystrobin (HIGH RISK)

Absolute, Acceleron, Adamant, Armada, Compass, Distinguish, Flint, Gem, Interface, Luna Sensation, Stratego, Tartan, Trilex

Triflumizole

Procure, Terraguard

Triforine

Orthenex, Rosepride

Triticonazole

Charter, Pillar, Reserve, Stamina, Trinity, Triton

Vinclozolin

Curalan, Touche

Ziram

Vancide, Ziram

Zoxamide

Gavel, Zoxium

*Trade product contains at least this sole active ingredient, but may be pre-mixed with additional active ingredients. Consult product label ingredient statements.

®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.

Footnotes

1.

This document is PI94, one of a series of the Pesticide Information Office, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date January 2006. Revised November 2012. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

F.M. Fishel, professor, Agronomy Department, and director, Pesticide Information Office; and M.M. Dewdney, assistant professor, Plant Pathology Department, Citrus Research and Education Center, Lake Alfred, FL; Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, 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.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.