WithTheGrain: Research shines light on fungicide resistance
Author: Alistair Lawson | Date: 13 Apr 2018
Investment by the GRDC is helping growers in the southern region to better understand the impact fungicide resistance may be having on their cropping systems.
Dr Fran Lopez-Ruiz leads the fungicide resistance group based at the Centre for Crop and Disease Management (CCDM) in Perth, Western Australia, a $100 million investment between the GRDC and Curtin University.
To date, there have been six cases of fungicide resistance and four cases of reduced sensitivity to fungicide – in which resistance does not reach the level of field failure of a fungicide application – in Australia (table 1).
Table 1: Fungicide resistance cases identified in Australia during the period 2012-2017.
|Barley powdery mildew||Group 3 (DMI)|
|Wheat powdery mildew||Groups 3* and 11 (QoI)|
|Barley net form net blotch||Group 3*|
|Barley spot form net blotch||Group 3|
|Canola blackleg||Groups 2 (MAP-Kinase) and 3*|
|Wheat septoria tritici blotch||Group 3*|
|Chocolate spot||Group 1 (MBC)|
|Ascochyta blight||Group 1|
*Reduced sensitivity that does not reach the level of field failure
Dr Lopez-Ruiz says many growers will experience a disappointing result with a commercial fungicide application which could be due to a number of reasons.
“It could be due to application technique, weather conditions unsuited to spraying or the particular product being applied,” he says.
“It is also possible that while the spray operator was following the label instructions, it might not have been appropriate for the situation such as the diseases present, the level of infection and the crop growth stage.
“In some cases, it could also be due to the build-up of resistance in the fungal pathogen population. The key issue with that is how growers respond to such a situation of failed disease control.
“Spraying again with a different fungicide may control the disease or it may make the resistance problem worse, especially if the second fungicide application is the same mode of action. Sometimes simply changing the fungicide product does not help the situation because actives used in different products are often the same.”
For this reason, Dr Lopez-Ruiz says it is very important to clearly identify the active being used and the mode of action it belongs to, which are commonly Groups 3, 7 and 11.
“Understanding how fungicide resistance occurs will enable us to minimise the impact and delay the worst effects,” he says.
Dr Lopez-Ruiz says the risk of fungicide resistance is greatest in pathogens with short latent periods, in pathogens with high levels of virulence against commonly grown crop varieties and when fungicides with a single mode of action are used.
“These conditions are often met in Australian crops where most diseases have short or very short latent periods, the level of virulence against some commonly used varieties are high and fungicides with the same mode of action are regularly applied during the growing season,” he says.
“Under this scenario, it is not surprising to find several diseases with high levels of resistance to fungicides, especially from Groups 3 and 11.”
High-risk pathogens in the southern region
Changes in the sensitivity of wheat powdery mildew (WPM) has come to light in high-rainfall areas of the southern region in recent years.
Samples of WPM from southern Victoria and Tasmania have been confirmed as having resistance to strobilurin chemistries such as azoxystrobin and pyraclostrobin, making it the first case of resistance to strobilurins or Quinone outside inhibitors (Group 11) recorded in broadacre cereal crops in Australia.
The resistant mutation is known as G143A – the same mutation found overseas – and was discovered by researchers at CCDM.
The latest information from CCDM indicates that the prevalence of the G143A mutant strains in the Tasmanian samples ranged between 9 per cent to 99 per cent with an average of 70 per cent, and 65 per cent in Victoria based on far fewer samples.
However, as these pathogen samples came from trials that had already been sprayed with strobilurin fungicide it is not indicative of the actual frequency in the field, since the sensitive strains will have been controlled.
Dr Lopez-Ruiz says the first step in managing fungicide resistance is to never compromise effective disease control. This includes careful chemical management.
“It is important that growers only apply fungicides when necessary, that they limit the number of applications per season and that they avoid repetitive uses of the same formulation in the same season,” he says.
“Tank mixing or alternating sprays with other modes of action is another effective chemical management strategy which will slow resistance.
“If growers are to spray for disease then protectant sprays should be applied before widespread infection. Waiting for a disease to become endemic will make it harder for the fungicide to work and increase the chances of resistance.”
Growers are also strongly encouraged to adopt an integrated disease management (IDM) strategy which will help to lessen their reliance on foliar fungicides.
An IDM strategy includes:
- Removing the green bridge
- Growing varieties with adequate genetic resistance against diseases
- Rotating crops
- Removing stubble
- Rotating fungicide modes of action and selecting fungicide mixtures with different modes of action wherever possible. Table 2 shows the CropLife Australia Fungicide Activity Group Table which outlines the different modes of action.
- Testing for resistance
Table 2: CropLife Australia fungicide activity group table (valid as at June 2017)
|FRAC code||Fungicide mode of action group||Chemical family||Active constituent||Trade name*|
|1||Methyl benzimidazole carbamates||Benzimidazole||carbendazim||various|
|thiabendazole||various e.g Tecto®|
|2||Dicarboximide||Dicarboximide||iprodione||various e.g. Rovral®|
|procymidone||various e.g. Sumisclex®|
|3||DMI||Imidazole||prochloraz||various e.g. Octave®|
|difenoconazole||various e.g. Score®, Dividend®|
|epoxiconazole||various e.g. Opus®|
|fluquinconazole||various e.g. Jockey®|
|flutriafol||various e.g. Armour®, Impact®|
|propiconazole||various e.g. Tilt®|
|tebuconazole||various e.g. Raxil®, Folicur®|
|triadimefon||various e.g. Bayleton®|
|triadimenol||various e.g. Bayfidan®, Baytan®|
|triticonazole||various e.g. Premis®|
|4||Phenylamide||Acylalanine||metalaxyl||various e.g. Ridomil®, Apron®|
|metalaxyl-m||various e.g. Ridomil® Gold, Apron XL®|
|7||SDHI (succinate dehydrogenase inhibitors)||Oxathiin carboxamides||carboxin||various e.g. Vitavax®|
|Pyrazole carboxamide||penthiopyrad||Fontelis Velista®|
|11||Quinone outside Inhibitors (QoI)||Methoxy acrylate||azoxystrobin||various e.g. Amistar®, Dynasty®|
|M3||Multi-site activity||Dithiocarbamate||mancozeb||various e.g. Dithane|
|thiram||various e.g. Thiram|
|propineb||various e.g. Antracol®|
|ziram||various e.g. Ziram|
|M5||Multi-site activity||Chloronitriles||chlorothalonil||various e.g. Bravo®|
- The table does not include active constituents that have not yet been assigned an activity group by CropLife Australia.
- Some products are mixtures of fungicides from activity groups. These appear only once in the table.
- If multiple trade names exist, the trade name entry is listed as various and the first registered trade name included.
Send in samples
Growers and advisers across the southern region are strongly encouraged to submit disease samples to CCDM this season to help map the spread of fungicide resistance in the southern region.
The results from these samples will help to inform the research community about not only the spread of fungicide resistance, but also help growers and advisers to adopt the appropriate fungicide strategy.
GRDC research codes: CUR00023, FAR00004-a, FAR00002, DAN00177
Dr Fran Lopez-Ruiz,
08 9266 3061,
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