Charles Sturt University (CSU) research has found a timely fungicide spray can help reduce the damage caused by non-Botrytis bunch rot in sub tropical vineyards.

The research, led by CSU Professor of Viticulture Chris Steel from the National Wine and Grape Industry Centre and funded by the Australian Grape and Wine Authority, has been published in the Australian Journal of Grape and Wine Research.

The most common form of bunch rot is Botrytis cinerea (grey mould) but Professor Steel said bitter rot and ripe rot can be just as damaging in sub tropical climates.

"We mainly see these fruit rots in areas which experience warm temperatures and wet conditions at harvest time, so primarily in vineyards north of Sydney, in the Hunter Valley, on the Mid-North Coast and into the Burnett region of Queensland," he said. "Occasionaly it can be a problem in the Mudgee area and even on the NSW South Coast near Eden."

Professor Steel, who teaches viticulture at CSU's School of Agricultural and Wine Sciences in Wagga Wagga NSW, said bitter rot and ripe rot can reduce yields and affect wine quality.

"Ripe rot is described as producing a hessian sack or mouldy straw flavour and both ripe rot and bitter rot can lead to a browning of red wine," he said. "Ripe rot also causes berries to shrivel and fall off."

Professor Steel said one of the key problems for growers is that there are no fungicides registered for controlling bitter and ripe rot in Australia and many of the practices used to manage Botrytis are ineffective.

As part of the research, fungicides used for controlling other diseases of grapes were screened in the laboratory to see if they were effective against the bitter and ripe rot fungi.

Field trials were then carried out on Chardonnay grapes in a commercial vineyard in the lower Hunter Valley from 2009 to 2012.

"We found that the application of the fungicide Cabrio at flowering and at veraison, independently and in combination,  reduced the incidence and severity of bitter and ripe rot at harvest.

"There were year-to-year differences,  particulary in the high rainfall year of 2012 when there was less control of bitter rot. Having said that there was still a significant reduction in the amount of bitter rot and ripe rot in all three years.

"The take-home message is that this product will work, but in some seasons when there's exceptionally wet weather then it may not be as effective," he said. "Variety selection and vineyard management can also play a key role in limiting the damage caused by non-Botrytis bunch rot."

A new project is focusing on understanding how bitter rot and ripe rot affect wine quality and what can be done in the production process to remove those flavours.

An audio interview with Professor Chris Steel is also available.