Research identifies growing fungicide resistance

Fungicide resistance across Australian vineyards is on the rise, with new research identifying higher–than–expected populations of powdery mildew, downy mildew and botrytis bunch rot with resistance.

Powdery mildew, downy mildew and botrytis bunch rot are the three most economically significant diseases in Australian viticulture – costing the sector in lost crops and disease management.

Wine Australia is funding a national collaborative research project with the South Australian Research and Development Institute (SARDI), Curtin University, The Australian Wine Research Institute (AWRI), National Wine and Grape Industry Centre, Department of Agriculture and Food Western Australia, University of Adelaide and several fungicide and viticulture companies to address this problem of resistance.

SARDI project leader Barbara Hall said the three and a half year project aims to better understand the mechanism for how resistance develops and determine the incidence and severity of resistant fungal populations in Australia.

‘We’ve also started work to determine the spread of resistant populations within a vineyard block using high-throughput next generation sequencing (via The AWRI) and we hope to develop and validate effective and sustainable resistance strategies for the at-risk fungicides’, Mrs Hall said.

‘We would also like to develop a rapid and accurate test for detection and quantification of resistance for all pathogen/fungicide combinations in vineyards to assist growers.

‘It’s still early days, so far we have completed only two seasons of sampling and testing.’

Core components of the project include collection of isolates from the field, phenotyping, genotyping, next generation, high-throughput sequencing and resistant strategy modelling.

Mrs Hall said resistance to the DMI and strobilurin fungicides (used to treat powdery mildew), metalaxyl (downy mildew) and DMI (botrytis) had been identified before the research project began, but field testing from vineyards across Australia revealed that it was more widespread than current data had shown.

‘For the first time we identified metalaxyl resistance in Tasmania and Western Australian vineyards’, she said.

‘There are also two vineyards where we identified populations resistant to the four most common fungicides used in treatment of botrytis bunch rot.

‘But just because we identified resistant strains it doesn’t automatically mean that the fungicide treatment will fail across the whole vineyard – there’s a lot more research and tests to be carried out before we can start quantifying what level of resistance leads to total field failure.

‘Essentially, right now, this data is a red flag – a warning that growers need to be very careful in their disease management strategies and to follow the label recommendations and recommended resistance management strategies.’