Yorke Peninsula barley growers should review their disease management practices after samples of a damaging fungal disease collected from local paddocks showed resistance to three widely used fungicide groups.
Barley is an important crop for South Australian grain growers. It is used in the production of beer and other foods, as well as in animal feed. But the disease 'net form net blotch' - caused by a fungus - can reduce its yield and grain quality.
As part of a Grains Research and Development Corporation (GRDC) investment, researchers analysed infected plant samples from three separate paddocks in Yorke Peninsula, at Corny Point, Warooka and Paskeville and, in Victoria, from a paddock at Streatham. The samples contained fungal isolates with genetic mutations associated with resistance or reduced sensitivity to the three fungicide groups (Groups 3, 7 and 11) currently available for controlling net form net blotch. Importantly, the disease in the Yorke Peninsula was not controlled by fungicide applications. This means that all three fungicide groups currently available to Yorke Peninsula barley growers are compromised for controlling net form net blotch.
Disease control in Streatham is not currently compromised but use of fungicides from these groups may encourage the selection and spread of the triple-resistant fungal disease population in those paddocks where it is present. Furthermore, any combination of fungicides may fail to adequately control the disease in barley paddocks where the triple-resistant fungus is present at high frequencies.
GRDC Crop Protection Manager - South, Ruth Peek, says growers can help protect barley yields for the coming season by eliminating all 'green bridge' volunteer barley, and consult with an agronomist about fungicide options for their specific local area.
Growers should also prioritise planning more non-barley rotations and choosing barley cultivars with improved net form net blotch resistance for subsequent years.
Associate Professor Fran Lopez-Ruiz, AFREN Project Lead at Curtin University, says the failure of fungicides to control net form net blotch on the Yorke Peninsula may be due to recently detected triple resistance mutations. Photo: CCDM Communications Team
Associate Professor Fran Lopez-Ruiz, Project Lead for the Australian Fungicide Resistance Extension Network (AFREN) based at Curtin University, coordinated the analysis of the samples. He agrees, the best approach is for growers to shift to newer barley cultivars with improved genetic resistance to net form net blotch, and to adopt agronomic disease management practices including rolling or grazing barley stubble and planting non-barley crop rotations.
Growers wanting to limit the chances of fungicide resistance developing can follow AFREN's Fungicide Resistance Five principles: 1) avoid susceptible crop varieties; 2) rotate crops; 3) use non-chemical control methods; 4) spray strategically and only if necessary; and 5) rotate and mix fungicides.
"Agronomy can be used to minimise disease pressure and reduce reliance on fungicides during the growing season. This reduces fungicide exposures that could encourage the development and spread of resistance," said Associate Professor Lopez-Ruiz.
"Even using fungicides to control other diseases of barley can select resistance in any net form net blotch pathogens that are also present. So, the only way to maximise the lifespan of existing fungicides is to rely on non-fungicide strategies to minimise disease.
"Group 3 and 7 fungicides have been compromised in net form net blotch for about five years. We have also been concerned about a mutation for resistance to Group 11 fungicides that was first detected in trials on the Yorke Peninsula in 2022.
We weren't surprised to find this Group 11 resistance when we tested the 2024 samples - but then we found mutations for Group 3 and 7 resistance in the same samples. We believe the observed failure to control disease of successive single and mixed fungicide applications, from multiple fungicide groups, are due to the combined triple resistance mutations.
Wind and splash dispersal can rapidly spread fungal spores containing resistance mutations. Typically, spores will travel short distances within the crop but can also be blown into neighbouring crops. Crucially, researchers consider it likely that the triple mutants are already present in surrounding paddocks.
AFREN is a Grains Research and Development Corporation (GRDC) investment to promote best practice management strategies for reducing the impact and emergence of fungicide resistance.
