Identification & Management of Field Crop Diseases in Victoria

  1. Home
  2. Docs
  3. Identification & Man...
  4. Fungicides
  5. Modes of Action

Modes of Action

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

Activity Group Code (FRAC Code)Fungicide Mode of Action GroupChemical FamilyActive IngredientType of ActivityMode of ActionRisk for Resistance
1Methyl Benzimidazole Carbamates (MBC)BenzimidazolesCarbendazim
Systemic with apoplastic mobility (protectant, curative)Inhibition of mitosis and cell divisionHigh
Systemic with apoplastic mobility (protective, curative)
Inhibition of lipids and membrane synthesisMedium to High
Inhibitors (DMI)
Triazoles 1Cyproconazole
Systemic with apoplastic mobility (protectant, curative, eradicant)Inhibition of sterol biosynthesis in membranesMedium
4Phenyl Amides (PA)Acylalanines 1Metalaxyl
Systemic (protectant, curative)Affect RNA synthesisHigh
7SDHI (Succinate dehydrogenase inhibitors)Oxathiin carboxamideCarboxin
Systemic (apoplastic mobility)Inhibits mitochondrial respiration (SDHIs)Medium
Pyridine carboxamideBoscalid
Pyrazole carboxamideSedexane
11Quinone Outside
Inhibitors (QoI)
Methoxy acrylateAzoxystrobin
Systemic activity with apoplastic + acropetal mobility (protectant, curative)Inhibition of mitochondrial respirationHigh
Oximino acetateKresoxim-methyl
Methoxy carbamatePyroclostrobin
12Phenylpyrroles (PPPhenylpyrrolesFludioxonilAffect proteins involved in membrane permeabilityLow to Medium
17HydroxyanilideHydroxyanilideFenhexamid^Inhibition of tubulin formation during mitosisHigh
M1Multi-site activityInorganicCopper 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 membersLow
M2Multi-site activityInorganicSulphur
Potassium bicarbonate
Calcium polysulfide
Contact (protectant)Act as multi inhibitors with several sites of action (sites may differ between group members)Low
M3Multi-site activityDithiocarbamateMancozeb
Contact (protectant)Act as multi inhibitors with several sites of action (sites may differ between group members)Low
M4Multi-site activityPhthalimideCaptan*Contact (protectant)Act as multi inhibitors with several sites of action (sites may differ between group members)Low
M5Multi-site activityChloronitrilesChlorothalonilContact (protectant)Act as multi inhibitors with several sites of action (sites may differ between group members)Low
1 Not a comprehensive list of actives. Only the most relevant actives listed here. For a full list visit
* 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 ActivityInhibits 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 ActivityInhibits 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 ActivityThese 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.
SystemicSystemic 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.
TranslaminarDescribe the movement of the fungicide from the sprayed to the unsprayed surface.

How can we help?