Triple fungicide resistance detected in YP barley

Analysis of the samples was coordinated by Curtin University-based Fran Lopez-Ruiz, project lead for the Australian Fungicide Resistance Extension Network.

Dr Lopez-Ruiz agrees the best approach is for growers to shift to newer barley cultivars with improved genetic resistance to NFNB, 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:

Avoid susceptible crop varieties;

Rotate crops;

Use non-chemical control methods;

Spray strategically and only if necessary; and,

Rotate and mix fungicides.

Dr Lopez-Ruiz said 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,” Dr Lopez-Ruiz said.

“Even using fungicides to control other diseases of barley can select resistance in any net form net blotch pathogens that are also present.

“The only way to maximise the lifespan of existing fungicides is to rely on non-fungicide strategies to minimise disease.

Dr Lopez-Ruiz said Group 3 and 7 fungicides have been compromised in NFNB 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 GRDC investment to promote best practice management strategies for reducing the impact and emergence of fungicide resistance.