Recent studies have detected more cases of resistance to succinate dehydrogenase inhibitor (SDHI) fungicide in the disease net form net blotch (NFNB).

In 2019, researchers identified dual resistance to both the SDHI seed dressing fungicide fluxapyroxad and some demethylation inhibitor (DMI) fungicides on farms affected by NFNB on South Australia's Yorke Peninsula (YP).

More incidences of SDHI resistance in NFNB have since been confirmed in samples from YP, and reduced sensitivity (reduction in the performance of the fungicide treatment that does not necessarily result in field failure) has been observed in samples collected on the border between South Australia and Victoria, as well as from Eyre Peninsula (EP).

The work has involved researchers from the Grains Research and Development Corporation (GRDC) and Curtin University co-invested Centre for Crop and Disease Management (CCDM), and the South Australian Research and Development Institute (SARDI).

The researchers have been working together to test samples collected from YP over recent months, as well as samples sent by SARDI collaborators, growers and agronomists.

Analysing barley samples collected from 15 locations on YP, the CCDM's fungicide resistance team has been able to paint a more detailed picture of the incidence of SDHI, DMI and dual resistance.

CCDM researcher Wesley Mair said: "Our previously released findings from 2019 showed that NFNB on YP was resistant to the SDHI seed dressing fungicide fluxapyroxad, and at the same time samples also showed resistance to the Group 3 DMI tebuconazole, which is a mixing partner in some DMI foliar fungicides."

"This latest testing now tells us that DMI resistance appears to be quite common, especially in the south of YP even though it hadn't been reported in SA previously."

According to the CCDM's fungicide resistance expert Fran Lopez-Ruiz, the testing of the more recent samples indicates that the SDHI resistance found on YP late last year is more widespread than first thought.

It is hoped the latest discoveries of reduced sensitivity to SDHI from outside YP will help to better inform growers about what to look for across the season.
SARDI plant pathologist Tara Garrard advised growers to be vigilant in watching for the disease and to put management strategies in place to help combat it.

"Anything we can help growers do to limit the amount of disease in the area is paramount and by taking the right steps they can help control resistance," Dr Garrard said.

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