Fungicide-resistant disease discovered

Fungicide-resistant disease discovered

Cropping
STRONG SAMPLES: The fungicide-resistant samples from Yorke Peninsula were identified by SARDI plant pathologists Tara Garrard and Hugh Wallwork. Photo: GRDC

STRONG SAMPLES: The fungicide-resistant samples from Yorke Peninsula were identified by SARDI plant pathologists Tara Garrard and Hugh Wallwork. Photo: GRDC

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AUSTRALIAN researchers have confirmed a new form of dual fungicide resistance in the common barley disease, net form net blotch.

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AUSTRALIAN researchers have confirmed a new form of dual fungicide resistance in the common barley disease, net form net blotch.

They have identified a new genotype in NFNB that is - for the first time known - showing dual resistance to both a succinate dehydrogenase inhibitor fungicide as well as some DeMethylation Inhibitor fungicides.

The discovery was outlined last week at the 2019 Crop Protection Forum at Moama in NSW.

Working together to test barley samples collected near Minlaton on the Yorke Peninsula, SARDI researchers and the Centre for Crop and Disease Management found fungal strains showing reduced fungicide sensitivity to SDHI fungicide fluxapyroxad.

The samples were identified by SARDI plant pathologists Tara Garrard and Hugh Wallwork and confirmed as resistant via tests conducted by CCDM's fungicide resistance team led by Fran Lopez-Ruiz.

"The samples, collected from two paddocks a short distance apart, clearly showed high NFNB disease levels when the SARDI team was first alerted to the problem by agronomist Sam Holmes," Dr Wallwork said.

Additional testing by the CCDM team then confirmed the higher levels of resistance correlated with a genetic mutation in the Sdh complex, which is the NFNB target of SDHI fungicides.

Following these initial tests more detailed studies were undertaken, reinforcing the discovery of resistance.

"While the type of SDHI resistance and the mutations found in the Yorke Peninsula isolates have been recorded previously in Europe, this is the first confirmation of this genotype in Australia," Dr Lopez-Ruiz said.

Dr Wallwork said the samples were from the barley variety Spartacus CL, grown in a barley-on-barley rotation with fluxapyroxad used in both years.

In terms of fungicide application, soil moisture in the area was considered to be adequate to allow for good uptake and further testing on residual seed clearly showed that the efficacy was greatly reduced.

Additional samples collected at the site also showed resistance to the Group 3 DMI fungicide tebuconazole, and although the resistance mechanism is still being investigated, Dr Lopez-Ruiz said it was known to be different to the DMI resistance mechanisms already reported in barley net blotches in WA.

The results are a reminder for growers to consider using different modes of action when applying fungicides, as continuous use of the same fungicides will increase selection pressure further, increasing the risk of even more rises in resistance levels. This also applies to the closely related spot form net blotch disease, which has already developed high levels of resistance to some DMIs in WA.

Growers on the YP should avoid using any SDHI fungicides for the control of NFNB on barley during 2020.

This will help to contain the further development of resistance and hopefully allow for the return of SDHI use in the region at a later date.

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