Clever diseases, such as the barley net blotches, require an equally clever management response. Accordingly, with GRDC investment the Centre for Crop and Disease Management (CCDM) at Curtin University has galvanised the WA grain industry in a unique co-innovation approach that is generating new insights for both the scientific understanding and management of this disease.

For two years the Barley Disease Cohort Project run by CCDM has invited growers from the southern WA grainbelt to work with CCDM researchers by sending in diseased barley leaves, answering survey questions on management decisions and being part of a cycle of co-innovation to find solutions for managing fungicide resistance.

The project has focussed on net blotch a common disease of barley, caused by the fungus Pyrenophora teres.  There are two forms of the fungus; spot form net blotch (P. teres f. maculata SFNB) and net form (P. teres f. teres NFNB). SFNB is more common and can cause significant production losses through reduced grain yield and quality, the extent of loss is dependent on the seasonal conditions and susceptibility of the barley variety. The net blotches can reproduce both asexually and sexually and also inter-hybridise making them complex and genetically diverse. This also means they are adept in responding to selection pressures such as the application of fungicides and therefore prime candidates to develop resistance.

“After two years of data collection across the southern grainbelt, it is clear that fungicide resistance in both net blotches is a very complex phenomenon,” says CCDM director, Professor Gibberd.

“However, the more we know about the diseases and the way growers manage them, the better we are placed to inform management decisions."

This is why co-innovating with growers on projects like this one is just so valuable.

Fungicide resistance

Associate Professor Fran Lopez-Ruiz leads the fungicide resistance team at CCDM and has been investigating fungicide resistance for several crop fungal diseases since 2002.

“Industry-wide surveillance of pathogens and how they are responding to management practices are vital for determining the efficacy and longevity of management interventions especially when it comes to fungicides,” Dr Lopez-Ruiz says.

There is power in numbers, in the data we can glean from the field to inform our science as well as grower’s management.

“We know that growers are using integrated management for net blotch, with barley varieties with increasing levels of tolerance and resistance as the foundation of their management, but we need to ensure that fungicides are used carefully.”

The fungicides used to control barley net blotch diseases belong to three major classes, demethylation inhibitor (DMI, FRAC Group 3), succinate dehydrogenase inhibitor (SDHI, FRAC Group 7) and quinone outside inhibitors (QoI, FRAC Group 11).

“From previous work we knew there was growing resistance to DMI and SDHI but not as yet QoI. Our interest was to determine just how extensive the resistance to DMI fungicides is across the southern WA grainsbelt.”

In 2020 growers collectively sent 115 diseased barley leaf samples to CCDM that were tested. This work was undertaken by Linda Thompson in conjunction with Dr Noel Knight.

“We were able to determine how these fungi grew on a concentration gradient of fungicides and could use this data to assess them as sensitive, reduced sensitivity or resistant.”

The spread of these response classes for Group 3 fungicides for 2020 is shown in Figure 1 for spot form net blotch. Reduced sensitivity and resistance were found in all the areas tested from Geraldton to Esperance, which suggests a high level of resistance selection across the grainbelt due to the overuse of DMI fungicides.

Figure 1: Distribution of spot form net blotch Group 3 fungicide resistance classes across southern WA in 2020.

Source: CCDM

“The extent of the spread and the complexity of the fungicide resistance means we need to tackle this as an industry through co-innovation, to preserve the fungicides we have available.”

The surveillance work continued in 2021 and samples are still being processed but are showing a growing pattern of spread.

“This surveillance work has prompted us to develop more sensitive genetic tests to quantify the amount of resistance to better inform management practices,” Dr Lopez-Ruiz says.

Awareness

Nutrien agronomist Kyran Brooks, based at Jerramungup, has been involved in the Barley Disease Cohort Project and says one of the significant achievements of the work is raising awareness with growers of the extent of fungicide resistance across southern WA.

“When we compare fungicide resistance to herbicide resistance it is less visual to growers as they can clearly see weeds that are able to withstand herbicide application,” Mr Brooks says.

With the number of growers contributing samples to CCDM’s work, growers have seen this ‘hidden’ problem and learnt that they are not alone if they have fungicide resistance.

“Growers have also learnt just how complex the disease is and that the science of identification is evolving,” Mr Brooks says.

“Growers are using integrated pest management strategies but this work of CCDM has emphasised the importance of using a variety of tools and that fungicides use should be minimised.”

“Real-time information for fungicide resistance would be a fantastic support for growers making fungicide application decisions during the growing season, but the service is not yet available.”

“As the development of new fungicides with new modes of action is a lengthy process, we need to preserve the efficacy of those we have available.”

Mr Brooks says this is why it is necessary to take an industry-wide approach to responsible use of fungicides.

How to best manage fungicide resistance:

• Rotate crops and manage stubble – avoid barley on barley.
• Plant less susceptible varieties – avoid S and VS varieties in disease prone areas.
• Fungicide management:
  • Minimise group 3 use: avoid using tebuconazole, propiconazole or epoxiconazole as stand-alone* products in barley for any disease, to avoid indirect fungicide resistance selection
  • Rotate group 3 actives within and across seasons
  • Avoid using more than 3 applications of fungicides that have a group 3 active, per season. If possible, reduce this to 2 applications in areas where group 3 resistance has been reported.
  • Minimise group 7 fungicide use. Do not use group 7 in areas where SFNB group 7 resistance has been reported (currently reported in the Cunderdin region).
  • Restrict group 7 and 11 fungicides to one application of each, per growing season
• Consider sowing later – early sowing can favour disease development and increase losses.

*Stand-alone application refers to use of the product by itself and not in a mixture.

More information: Associate Professor Fran Lopez-Ruiz, fran.lopezruiz@curtin.edu.au

Read also: Fungicide resistance management in Australian grain crops; and Net blotch fungicide resistance profiling enriches knowledge base.