Triple stacked fungicide resistance detected in barley for the first time

Fran Lopez-Ruiz, AFREN, says growers need to look at more than just chemical measures to control net form of net blotch. File photo.

Barley producers across the country are being warned to monitor their crops for signs of fungicide resistance this season.

Subscribe now for unlimited access.

or signup to continue reading

All articles from our website

The digital version of This Week's Paper

Our entire network

The warning from the Grains Research and Development Corporation (GRDC) comes after the finding of the existence of net form of net blotch (NFNB) on South Australia's Yorke Peninsula with resistance to the only three major fungicide groups registered for use on the disease.

Researchers analysed infected plant samples from three separate paddocks in different areas on the Yorke Peninsula, at Corny Point, Warooka and Paskeville and, in Victoria, from a paddock at Streatham in the state's Western District.

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 NFNB.

On the Yorke Peninsula the disease was not controlled by fungicide applications, meaning growers have no product available without compromised control.

The situation was slightly less serious at Streatham, where the researchers reported that disease control in Streatham was 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, they said 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, said that with pressure on fungicide, paddock management would play a key role in minimising the risk of the disease and protect yields.

She advised growers to control any summer 'green bridges' of volunteer barley and to prioritise non-barley options in the rotation.

If they were to grow barley Ms Peek advised the use of varieties with a strong NFNB disease resistance rating.

Associate Professor Fran Lopez-Ruiz, Project Lead for the Australian Fungicide Resistance Extension Network (AFREN) based at Curtin University, in Western Australia coordinated the analysis of the samples.

He agreed with Ms Peek on the merits of using resistant varieties.

"The best approach is for growers to shift to newer barley cultivars with improved genetic resistance to net form net blotch," Prof Lopez-Ruiz said.

He also suggested several agronomic practices that could help, including rolling or grazing barley stubble and pointed growers wanting to limit the chances of fungicide resistance to AFREN's Fungicide Resistance Five principles which are:

Avoid susceptible crop varieties;

Rotate crops

Use non-chemical control methods;

Spray strategically and only if necessary

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," he said.

Prof Lopez-Ruiz warned farmers to think of their fungicide rotations holistically and not just in terms of one specific disease.

"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.

He said there had been a gradual reduction in the efficacy of available fungicides and that the stacked resistance was a concern.

"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."

Prof Lopez-Ruiz said that with wind and splash dispersal of the spores of the disease it can easily transfer from paddock to paddock over short distances.