Triple fungicide resistance confirmed in Yorke Peninsula barley

Triple fungicide resistance has been detected in net form net blotch (NFNB) infections in barley crops on South Australia’s Yorke Peninsula, prompting researchers and industry bodies to call for urgent changes to disease management strategies.

Plant samples taken from barley paddocks at Corny Point, Warooka and Paskeville contained fungal isolates resistant to all three fungicide groups registered for controlling NFNB – Groups 3, 7 and 11. These findings, based on genetic analysis funded by the Grains Research and Development Corporation (GRDC), confirm that current fungicide options are no longer effective in suppressing the disease in affected fields.

Associate Professor Fran Lopez-Ruiz, project lead of the Australian Fungicide Resistance Extension Network (AFREN) at Curtin University, said the combination of mutations in the Yorke Peninsula samples renders single and mixed fungicide applications ineffective. “We believe the observed failure to control disease with successive fungicide applications is due to the presence of triple resistance mutations,” Lopez-Ruiz said.

Fungal spores containing resistance mutations can spread quickly within and between crops via wind and rain splash, raising concerns that resistant populations may already be established across wider areas of the region.

While a similar fungal strain was detected in Streatham, Victoria, fungicide control has not yet failed there. However, researchers caution that continued use of the same fungicide groups may encourage resistance development in those paddocks.

GRDC Crop Protection Manager for the southern region, Ruth Peek, urged growers to adopt integrated disease management practices immediately. “Barley growers should eliminate green bridge hosts, consider rotating away from barley, and use cultivars with improved resistance to net form net blotch,” she said.

Lopez-Ruiz recommended following AFREN’s ‘Fungicide Resistance Five’ guidelines: avoid susceptible varieties, rotate crops, use non-chemical controls, apply fungicides only when necessary, and rotate or mix fungicide modes of action.

Resistance to Group 3 and Group 7 fungicides in NFNB has been known in South Australia for several years. However, resistance to Group 11 fungicides was first detected in Yorke Peninsula trials in 2022 and has now been confirmed to co-occur with the other two resistance types.

AFREN and GRDC continue to promote strategies aimed at reducing fungicide resistance and sustaining disease control tools. Industry experts warn that without significant changes to current practices, the spread of multi-resistant NFNB strains could severely limit future control options and reduce barley productivity across the region.