Fungicides prevent fungal growth by interfering with critical cellular processes within the fungus and how a fungicide affects a fungus is called its mode of action. Fungicides are divided into activity groups based on their mode of action. Most fungicides used in field crops in Australia are within five chemical groups (groups 1, 2, 3, 7 and 11) and are described as follows:
Group 1 – Benzimidazoles
These products provide protective and curative control and show translaminar mobility. Mode of action is by inhibiting mitosis, more specifically, by binding the tubulin needed for cell and nuclear division thus resulting in death of the fungus. Examples include the active ingredients carbendazim and thiabendazole, which are used as pulse fungicides
Group 2 – Dicarboximides
Many of the pulse fungicides fall within this group (e.g. active ingredients iprodione and procymidone). Dicarboximides are systemic fungicides with both preventive and curative activity. These fungicides act on the fungi by inhibiting spore germination and affecting cell division. The benefits of these products are that they control a unique group of fungi including botrytis and sclerotinia.
Group 3 – Demethylation inhibitors (DMI) – Triazoles
Triazoles are de-methylation inhibitors (DMI) which prevent ergosterol biosynthesis. Triazoles have systemic activity and provide protective, curative and eradicant control. Examples include the active ingredients propiconazole, tebuconazole, triadimenol, triadimefon, triticonazole, and epoxyconazole.
Group 7 – Succinate Dehydrogenase Inhibitors (SDHI)
SDHIs are locally systemic, movement is translaminar and upward. In Australia, SDHIs are mainly used as seed treatments either on their own or in combinations with other chemical groups. SDHIs inhibit cellular energy production. Examples include carboxin, penflufen, fluxapyroxad or seed treatments combining difenoconazole (Group 3), metalaxyl-m (Group 4) and sedaxane (Group 7). Foliar fungicide formulations including SDHIs have recently been released to the Australian market e.g. bixafen and adepidyn.
Group 11 – Quinone Outside Inhibitor (QoI) – Strobilurins
QoIs contain the strobilurins which are preventative and locally systemic (translaminar). QoIs inhibit cellular energy production. Some Qols, like azoxystrobin can move in the xylem. They are generally mixed with triazoles for agricultural use in Australia to reduce the chance of resistance.
Fungicide chemical groups for resistance management and related information (adapted from CropLife www.croplife.org.au)
| Activity Group Code (FRAC Code) | Fungicide Mode of Action Group | Chemical Family | Active Ingredient | Type of Activity | Mode of Action | Risk for Resistance |
|---|---|---|---|---|---|---|
| 1 | Methyl Benzimidazole Carbamates (MBC) | Benzimidazoles | Carbendazim Thiabendazole | Systemic with apoplastic mobility (protectant, curative) | Inhibition of mitosis and cell division | High |
| Thiophanates | Thiophanate-methyl | |||||
| 2 | Dicarboximides | Dicarboximides | Iprodione Procymidone | Systemic with apoplastic mobility (protective, curative) | Inhibition of lipids and membrane synthesis | Medium to High |
| 3 | Demethylation Inhibitors (DMI) | Triazoles 1 | Cyproconazole Difenoconazole Epoxiconazole Fluquinconazole Flutriafol Ipconazole Propiconazole Prothioconazole Tebuconazole Triadimefon Triadimenol Triticonazole | Systemic with apoplastic mobility (protectant, curative, eradicant) | Inhibition of sterol biosynthesis in membranes | Medium |
| 4 | Phenyl Amides (PA) | Acylalanines 1 | Metalaxyl Metalaxyl-M | Systemic (protectant, curative) | Affect RNA synthesis | High |
| 7 | SDHI (Succinate dehydrogenase inhibitors) | Oxathiin carboxamide | Carboxin Oxycarboxin | Systemic (apoplastic mobility) | Inhibits mitochondrial respiration (SDHIs) | Medium |
| Pyridine carboxamide | Boscalid | |||||
| Pyrazole carboxamide | Sedexane Penflufen Fluxapyroxad Bixafen |
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| 11 | Quinone Outside Inhibitors (QoI) (Strobilurins) | Methoxy acrylate | Azoxystrobin Famoxadone | Systemic activity with apoplastic + acropetal mobility (protectant, curative) | Inhibition of mitochondrial respiration | High |
| Oximino acetate | Kresoxim-methyl Trifloxystrobin |
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| Methoxy carbamate | Pyroclostrobin | |||||
| 12 | Phenylpyrroles (PP | Phenylpyrroles | Fludioxonil | Affect proteins involved in membrane permeability | Low to Medium | |
| 17 | Hydroxyanilide | Hydroxyanilide | Fenhexamid^ | Inhibition of tubulin formation during mitosis | High | |
| M1 | Multi-site activity | Inorganic | Copper cuprous oxide Copper hydroxide Copper oxychloride Copper ammonium acetate Tribasic copper sulphate Copper octanoate | Contact (protectant) | Act as multi inhibitors with several sites of action (sites may differ between group members | Low |
| M2 | Multi-site activity | Inorganic | Sulphur Potassium bicarbonate Calcium polysulfide | Contact (protectant) | Act as multi inhibitors with several sites of action (sites may differ between group members) | Low |
| M3 | Multi-site activity | Dithiocarbamate | Mancozeb Metiram Thiram Propineb Zineb Ziram | Contact (protectant) | Act as multi inhibitors with several sites of action (sites may differ between group members) | Low |
| M4 | Multi-site activity | Phthalimide | Captan* | Contact (protectant) | Act as multi inhibitors with several sites of action (sites may differ between group members) | Low |
| M5 | Multi-site activity | Chloronitriles | Chlorothalonil | Contact (protectant) | Act as multi inhibitors with several sites of action (sites may differ between group members) | Low |
* Permitted use only (PER81406)
^ Permitted use only (PER14211)
Definitions for terms to describe fungicide activity and mobility
| Types of Fungicide Activity/Mobility | Description |
|---|---|
| Protective / Preventative Activity | Inhibits spore germination or kills germinating spores on the plant surface. Protectant fungicides must be applied to the plant prior to the arrival of the pathogen, or at least before it has a chance to germinate and enter its host. Coverage is very important because the fungicide must be in contact with the spore to be effective; hence new tissues from actively growing plants will not be protected. The majority of fungicides used in field crops in Victoria are in this category. |
| Curative Activity | Inhibits fungal growth prior to symptoms appearing but can be effective on fungi once they’ve infected the host. Curative activity is limited to the early part of the incubation period, likely only for the first 24 to 36 hours after spore germination and infection. Curative products do not repair tissue that has already been damaged or killed by the fungus. Many fungicides fall within this category. |
| Eradicant Activity | These fungicides have the ability to limit growth and spore production even after symptoms are visible. Some fungicides fall within this category. Examples include those active ingredients in the triazole family, e.g. propiconazole, tebuconazole, and triadimefon. |
| Systemic | Systemic fungicides are able to penetrate the plant. They show mobility via phloem. |
| Contact (non-systemic) | These fungicides do not penetrate the plant. Typically they are not redistributed and their action is restricted to the treated foliage. |
| Translaminar | Describe the movement of the fungicide from the sprayed to the unsprayed surface. |
