Fungicide Use in Field Crops: Web Book

2.1: FRAC Codes 1 - 21

2.1: FRAC Codes 1 - 21

Click on a FRAC code below to navigate directly to field crop-related information for that code. For FRAC codes 22-M, see the next section.

 

FRAC Code 1 - Methyl Benzimidazole Carbamate (MBC) Fungicides

FRAC Code 2 - Dicarboximide Fungicides

FRAC Code 3 - Demethylation Inhibitor (DMI) Fungicides 

FRAC Code 4 - Phenylamide Fungicides

FRAC Code 7 - Succinate Dehydrogenase Inhibitors (SDHI) Fungicides

FRAC Code 9 - Anilio-pyrimidine (AP) Fungicides

FRAC Code 11 - Quinone Outside Inhibitor (QoI) Fungicides

FRAC Code 12 - Phenylpyrrole (PP) Fungicides

FRAC Code 14 - Aromatic Hydrocarbon (AH) Fungicides

FRAC Code 21 - Quinone Inside Inhibitor (QiI) Fungicides

 

FRAC Code 1 - Methyl Benzimidazole Carbamate (MBC) Fungicides

Group Name and Chemical Group: The methyl benzimidazole carbamate (MBC) fungicide group contains the benzimidazole and thiophanate chemical groups, such as thiophanate-methyl.

Mode of Action and Target Site: Cytoskeleton and motor protein: Inhibits β-tubulin production, interfering with normal cell division in sensitive fungi. 

Phytomobility: While these fungicides have systemic properties, they cannot move down in the plant, making complete plant coverage essential for control. 

Role in Plant Protection: These fungicides have preventive and early-infection activity. 

Spectrum: MBC fungicides are effective against a broad range of fungi that cause leaf spots, root and crown rots, stem rots, and powdery mildews, but are not effective on rust fungi.

Risk for Resistance: The modification of a single amino acid in a fungus can result in resistance. Resistance to these fungicides was first reported in 1970. Many important fungal plant pathogens have become resistant to these fungicides. The MBC fungicide risk of resistance is HIGH. 

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FRAC Code 2 - Dicarboximide Fungicides

Group Name and Chemical Group: The dicarboximide group contains only the dicarboximide chemical group, which includes, but is not limited to, iprodione and vinclozolin. 

Mode of Action and Target Site: Signal transduction: Inhibits fungal growth by affecting osmotic regulation in fungal cells and disrupting membrane function. 

Phytomobility: Fungicides in this group are locally systemic, accumulating in the waxy cuticle with translaminar movement to the other side of the leaf. These fungicides are not translocated in the water-conducting elements of the plant (xylem). Complete plant coverage is essential to maximize control. 

Role in Plant Protection: Preventive and early-infection activity. 

Spectrum: Dicarboximide fungicides are effective against a limited range of fungi. 

Risk of Resistance: Fungicide resistance is common in many fungi for this group of fungicides. Single mutations can lead to fungicide resistance to this group, and cross-resistance is common. Dicarboximide risk of resistance is MEDIUM to HIGH.

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FRAC Code 3 - Demethylation Inhibitor (DMI) Fungicides

Group Name and Chemical Group: The demethylation inhibitors (DMI) fungicide group includes important chemical groups such as the triazole and triazolinthione fungicides, but also includes the piperazines, pyridines, pyrimidines, and imidazoles. Examples of active ingredients used on field crops include prothioconazole and propiconazole.

Mode of Action and Target Site: Sterol biosynthesis in membranes: These fungicides work by inhibiting a specific enzyme that plays a role in sterol production in fungi. Sterols are necessary for the development of functional cell membranes in fungi. Application of DMIs results in abnormal fungal growth and death. However, triazoles have no effect on spore germination because spores contain enough sterol for the formation of germ tubes. 

Phytomobility: DMI fungicides are acropetally mobile, meaning that they are taken up into the plant and can move short distances in the water-conducting elements (xylem) of plants.

Role in Plant Protection: DMI fungicides must be applied preventively or at early infection to be effective. 

Spectrum: DMI fungicides are highly effective against powdery mildews, rusts, and many leaf spotting fungi. 

Risk of Resistance: DMI fungicides have a very specific site of action, so the risk of resistance development is a concern. Reduced sensitivity to certain DMI fungicides has been reported in several U.S. states for Fusarium graminearum on wheat. Resistance management practices include avoiding repeated applications of DMI fungicides in the same season against high-risk pathogens such as those that cause powdery mildews. The DMI fungicide risk of resistance is MEDIUM. 

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FRAC Code 4 - Phenylamide Fungicides

Group Name and Chemical Group: The phenylamide group contains the chemical groups, acylalanines, butyrolactones, and oxazolidinones. Within the acylalanines chemical group are the widely used fungicides metalaxyl and mefenoxam. 

Mode of Action and Target Site: Nucleic acids metabolism: Fungicides within this group interfere with critical enzymes for building proteins for cell structure and regulation. When these enzymes are inhibited, pathogen growth slows or stops. This group is commonly used against oomycete pathogens. 

Phytomobility: Fungicides within this group are acropetally mobile and can be translocated in the xylem toward leaf tips. 

Role in Plant Protection: Fungicides in this group are capable of preventing further development of existing infections (kickback) but work best as preventives. 

Spectrum: In field crops the spectrum of activity is narrow, focused mostly on oomycete pathogens, such as Pythium and Phytophthora spp.

Risk of Resistance: Resistance and cross-resistance has been well documented in oomycete pathogens, but the mechanism leading to this resistance is unknown. The phenylamide fungicide risk of resistance is HIGH.   

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FRAC Code 7 - Succinate Dehydrogenase Inhibitors (SDHI) Fungicides

Group Name and Chemical Group: Succinate dehydrogenase inhibitors (SDHI) fungicides include several important chemical families such as the carboximides and benzamides. Within these broad chemical families are 11 different chemical groups, including but not limited to, the pyridine-carboximide, pyrazole-4-carboximides, pyridinyl-ethyl-benzamides, and phenyl-benzamides. Some common active ingredients used in field crops are boscalid, carboxin, flutolanil, fluopyram, and penthiopyrad.

Mode of Action and Target Site: Respiration: Fungicides in these chemical groups inhibit the respiration of target fungi, specifically complex II of fungal respiration. 

Phytomobility: SDHI fungicides are acropetally mobile fungicides, meaning that they are taken up into the plant and can move short distances in the water-conducting elements (xylem) of plants.

Role in Plant Protection: SDHI fungicides are excellent when used preventively and can inhibit early infections. 

Spectrum: Reasonably broad; although some target specific pathogens. For example, boscalid is primarily a foliar fungicide used against Botrytis, Sclerotinia, and Alternaria pathogens. 

Risk of Resistance: Resistance has been documented for these fungicides. The SDHI fungicide risk of resistance is MEDIUM to HIGH. 

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FRAC Code 9 - Anilio-pyrimidine (AP) Fungicides

Group Name and Chemical Group: The anilio-pyrimidines (AP) chemical group contains fungicides such as cyprodinil and pyrimethanil.

Mode of Action and Target Site: Amino acids and protein synthesis: Fungicides in this group inhibit production of amino-acids in fungal pathogens and specifically inhibit fungal penetration and subsequent growth in the host plant.

Phytomobility: AP fungicides are acropetally mobile, capable of moving upward in the water-conducting elements (xylem) of the plant, toward leaf tips. 

Role in Plant Protection: AP fungicides should be considered protectants and are most effective when applied before infection takes place. 

Spectrum: Active against species of Botrytis and several other genera.

Risk of Resistance: Resistance to AP fungicides has been documented in species of Botrytis and Venturia. The AP fungicide risk of resistance is MEDIUM.

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FRAC Code 11 - Quinone Outside Inhibitor (QoI) Fungicides

Group Name and Chemical Group: The Quinone outside inhibitor (QoI) group contains nine chemical groups including several significant ones, such as the methoxy-acrylates, methoxy-carbamates, and oximino-acetates. Examples of commonly used QoI fungicides include pyraclostrobin and azoxystrobin. Certain QoI fungicides are sometimes referred to as strobilurin fungicides, although this terminology is outdated and not encouraged. 

Mode of Action and Target Site: Respiration: Fungicides in this group inhibit mitochondrial respiration, specifically complex III at the Qo site, effectively stopping energy production of the fungus, and resulting in death. 

Phytomobility: QoI fungicides have varied phytomobility. Some are locally systemic, while others are acropetally mobile.

Role in Plant Protection: QoI fungicides are effective on spore germination and early growth. QoI fungicides are not effective against fungi that are growing inside the leaf tissue, so they must be applied preventively or at early infection to be effective. These fungicides have approximately 7-21 days of residual activity. 

Spectrum: QoI fungicides are very effective against a broad spectrum of fungi. 

Risk of Resistance: QoI fungicides have a very specific site of action, so the risk of resistance development is high. Currently there are more than 20 plant pathogens with some level of resistance to QoI fungicides. The Qol fungicide risk of resistance is HIGH. 

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FRAC Code 12 - Phenylpyrrole (PP) Fungicides

Group Name and Chemical Group: The phenylpyrroles (PP) contain the phenylpyrroles chemical group. The main fungicide used in field crops in the PP group is fludioxonil, which is used as a seed treatment and also as a foliar fungicide in some field crops.

Mode of Action and Target Site: Signal transduction: Fludioxonil affects osmotic regulation in some fungi. Reduced osmotic regulation results in bursting of the fungal cell, which thereby prevents fungal growth.

Phytomobility: Fludioxonil is locally systemic, accumulating in the waxy cuticle and moving from one side of the leaf to another (translaminar movement). These fungicides are not translocated in the water-conducting elements of the plant (xylem).

Role in Plant Protection: Fludioxonil should be used preventively. In addition, using spray technology that maximizes coverage on the plant may help maximize control using this fungicide.

Spectrum: Fludioxonil is effective against a broad spectrum of fungi.

Risk of Resistance: Resistance to this fungicide has been documented in a limited number of fungi. The PP fungicide risk of resistance is LOW to MEDIUM.

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FRAC Code 14 - Aromatic Hydrocarbon (AH) Fungicides

Group Name and Chemical Group: The aromatic hydrocarbons (AH) group contains the aromatic hydrocarbon group and heteroaromatics. In field crops, fungicides of interest that fall in the AH chemical group are usually included on seed treatments, such as tolclofos-methyl.  

Mode of Action and Target Site: Lipid synthesis or transport/membrane integrity function: The specific target site of AH fungicides such as chloroneb is uncertain. However, there is evidence to suggest that the AH fungicides cause a breakdown of certain lipids in the cell membrane. 

Phytomobility: Phytomobility of AH fungicides is considered low. Chloroneb is considered a primarily contact fungicide with very limited absorption into plant tissue.  

Role in Plant Protection: AH fungicides should be used as preventives as they are unlikely to be able to suppress an existing infection.

Spectrum: In field crops the spectrum of control is relatively narrow, directed toward soilborne organisms. AH fungicides are typically used as in-furrow or seed-treatments in field crops.

Risk of Resistance: Resistance is known in some fungi. Cross-resistance is complicated due to different spectra of activity within the group. The AH fungicide risk of resistance is LOW to MEDIUM.

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FRAC Code 21 - Quinone Inside Inhibitor (QiI) Fungicides

Group Name and Chemical Group: The quinone inside inhibitors (QiI) group consists of three chemical groups, cyano-imidazole, sulfamoyl-triazole, and picolinamides. In field crops, the cyano-imidizole group is of importance as it contains the fungicide cyazofamid. Cyazofamid is an important fungicide for the control of late blight on potato, which is caused by an oomycete organism.

Mode of Action and Target Site: Respiration: QiI fungicides function by disrupting electron transport in mitochondrial respiration. This process is similar to that of the QoI fungicides, except that the specific target site of QiI fungicides is different than that of the QoI fungicides, on the electron transport chain (specifically on the Qi site).

Phytomobility: Cyazofamid is locally systemic and exhibits translaminar movement (see section 1.3). Cyazofamid is not translocated in the water-conducting elements of the plant (xylem).

Role in Plant Protection: QiI fungicides like cyazofamid should be used preventively. However, QiI fungicides are capable of early-infection activity. 

Spectrum: The spectrum of control of QiI fungicides in field crops is fairly narrow, and targeted toward oomycete pathogens.

Risk of Resistance: No cases of QiI resistance are known. However, the QiI fungicide risk of resistance is assumed to be MEDIUM to HIGH.

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2.1: FRAC Codes 1 - 21