Courtesy: GRDC Ground Cover, original article published online – Fungicides available for Australian grain crops and their modes of action | Groundcover (grdc.com.au)
Fungicides play a critical role in safeguarding Australian grain crops, ensuring healthy yields and maintaining food security. As one of the world’s leading exporters of grains such as wheat and barley, Australia relies on effective fungicide strategies to combat fungal diseases that can devastate crops.
Fungal diseases such as rusts and net blotches can quickly spread and decimate entire fields. In a country where climate variability is a constant challenge, timely and effective disease management is essential.
This is where correct fungicide application along with best disease management practices are vital to support a successful yield for the grower and ensure the longevity of fungal chemistries.
Fungicides work through various modes of action (MoA) to combat fungal pathogens. These MoA determine how the fungicide interacts with the fungal pathogen and ultimately prevents or manages the disease. Understanding MoA is crucial for growers and agronomists when selecting and applying fungicides effectively.
Fungicides are categorised according to their MoA and assigned to an internationally determined group number. When a fungal pathogen develops resistance to a particular fungicide, it often puts all other fungicides belonging to the same MoA group at risk of reduced effectiveness, or the development of resistance.
Globally, more than 200 fungicides are approved for the management of fungal pathogens in agriculture, classified into 57 different MoA groups. However, in the context of Australian grain crop protection, only a limited number of these MoA groups are registered, and a select few dominate the market (Tables 1 and 2).
Table 1: Dominant MoA groups used in Australian grain crops.
Source: Fungicide Resistance Management in Australian Grain Crops
| Group | Common active ingredient | Target | Registered for use on these listed crops | Risk of resistance |
|---|---|---|---|---|
| Group 3 Azoles/demethylase inhibitors (DMIs) | cyproconazole, epoxiconazole, flutriafol, tebuconazole, propiconazole, prothioconazole, triadimefon. | Inhibition of cell membrane synthesis. These fungicides interfere with the production of ergosterol, a vital component of fungal cell membranes. By disrupting the integrity of fungal membranes, sterol inhibitors weaken the pathogen and inhibit its growth. | Canola, cereals and pulses. Used as a seed dressing, and as a mixing partner in some foliar formulations. | Moderate |
| Group 7 Succinate dehydrogenase inhibitors (SDHIs) | bixafen, fluxapyroxad, penflufen. | Interference with respiration. These fungicides disrupt the energy production process of fungi (also known as respiration), depriving them of essential energy to germinate and grow. | Canola, cereals and pulses. Used as a seed dressing, and as a mixing partner in some foliar formulations. | Moderate to high |
| Group 11 Strobilurins/quinone outside inhibitors (QoIs) | azoxystrobin, pyraclostrobin. | Interference with respiration. Similar to Group 7, QoI fungicides work by inhibiting the fungus’s ability to produce energy through normal respiration. | Canola, cereals and pulses. Used as a mixing partner in foliar and in-furrow formulations. | High |
This limited availability of fungicide groups increases the risk of fungicide resistance emergence because growers have very few alternatives to rotate with, which would otherwise help mitigate the selection pressure on these fungicide MoA groups.
While fungicides are invaluable tools in grain crop protection, their overuse or improper application can lead to the development of resistance in fungal populations.
Table 2: Other MoA Groups registered for Australian grain crop diseases.
Source: Fungicide Resistance Management in Australian Grain Crops
| Group | Common active ingredient | Target | Registered for use on | Risk of resistance |
|---|---|---|---|---|
| Group 1 Methyl benzimidazole carbamates (MBCs) | carbendazim, thiabendazole | Interference with cell division: cytoskeleton and microtubule arrested; failure in cell division leading to cell death. | Pulses. | High |
| Group 2 Dicarboximides/MAP-kinase inhibitors | iprodione | Signal transduction: disruption of osmoregulation and membrane function that inhibit fungal growth. | Canola (not for blackleg) and pulses (excluding chickpeas). | Moderate |
| Group 4 Phenylamides/PAA | metalaxyl | Nucleic acid metabolism: Disrupt key enzymes needed to construct cell proteins for structure and control. Growth of fungus is slowed down or interrupted. | Most crops. Used as a mixing partner in seed treatments and in-furrow applications to target oomycetes (e.g. Phytophthora spp., Pythium spp.). | High |
| Group 5 Amines/Morpholines | spiroxamine | Inhibit metabolism: Disrupt the fungal pathogen’s ability to generate energy, leading to impaired growth; morpholines target sterol biosynthesis, a component required for cell membrane integrity. | Barley. | Low to moderate |
| Group 12 Phenylpyrroles/PP fungicides | fludioxonil | Signal transduction: Reduces osmoregulation, preventing fungal growth. | Canola, maize, peanut and sorghum | Low to moderate |
| Group 13* Azanaphthalene | quinoxyfen, proquinazid | Signal transduction and cell membrane disruption: inhibit the function of an enzyme that is critical for cell membrane integrity. | Barley, wheat* | Moderate |
| Group 14 Aromatic hydrocarbons and heteroaromatics | quintozene | Disruption of lipid synthesis, transport and membrane integrity. | Peanuts (soil-borne fungi). | Low to moderate |
| Group 33 Phosphonates | phosphorus acid | Disruption of cell membrane: compromised cell membrane integrity weakens the fungal pathogen, making it more susceptible to environmental stressors. | Barley, canola and wheat. Principally used for the control of oomycetes (e.g. Phytophthora spp., Pythium spp.). | Low |
| Group 50* Actin disruption aryl-phenyl-ketones | metrafenone | Disruption of the cytoskeleton and motor protein: loss of cell integrity and function. | Wheat* | Moderate |
| M1-M5 Multi-site activity | chlorothalonil, copper, mancozeb, sulfur | Chemicals with multi-site activity: affect multiple biochemical sites in fungal pathogens. | Predominantly pulses. Good rotation and mixing partner options for managing fungicide resistance. | Low |
*currently only available under a Minor Use Permit for the control of wheat powdery mildew.
PER93197 Legend® (quinoxyfen) / Wheat / Powdery Mildew, permit end date 31 July 2024
PER93198 Vivando® (metrafenone / Wheat / Powdery Mildew, permit end date 31 July 2024
PER93216 Talendo® (proquinazid) / Wheat / Powdery Mildew, permit end date 31 July 2024
How can we prevent the emergence of fungicide resistance? Simple: stop the fungus from adapting to the treatments applied. This can be achieved by regularly changing the types of fungicide chemistries used, or mixing fungicides from different MoA groups.
Properly implemented fungicide rotations are crucial when incorporating fungicides with specific MoAs into disease management programs. It is essential to strictly adhere to fungicide labels and ensure that certain fungicide chemistries are not excessively employed to maintain their long-term effectiveness.
To combat resistance, GRDC supports the operation of the Australian Fungicide Resistance Extension Network. This network provides information and support for growers and advisers to manage fungicide resistance. AFREN strongly encourages growers to implement the AFREN Fungicide Resistance Five integrated disease management (IDM) strategies.
- Avoid susceptible crop varieties
- Rotate crops – use time and distance to reduce disease carry-over
- Use non-chemical control methods to reduce disease pressure
- Spray only if necessary and apply strategically
- Rotate and mix fungicides/mode of action groups
Additional information
Fungicides are approved based on factors such as state/territory, crop, target pathogen, formulation and application rate. Up-to-date details regarding registered fungicides and their applications can be accessed through the APVMA website at apvma.gov.au.
The mentioned risk of resistance development is determined through global observations and evaluations conducted by the international Fungicide Resistance Action Committee (FRAC). For further insights, refer to the FRAC website at frac.info. For an overview of MoAs as it relates to the Australian grains industry, visit AFREN.com.au and under the Resources tab locate the Fungicide Resistance Management in Australian Grain Crops Guide.
More information: Associate Professor Fran Lopez-Ruiz, AFREN project manager and fungicide resistance team leader at the CCDM, Curtin University, fran.lopezruiz@curtin.edu.au