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Managing botrytis this season

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article image Botrytis costs the Australian wine industry an estimated $52 million per annum. Photo by Dr Katherine Evans, TIA

The use of boscalid fungicide has been restricted on grapes for export wines this season. AWRI’s 2013-14 list of fungicides for use in Australian viticulture has changed boscalid use to ‘not recommended for use on grapes destined for export wines’.

This season’s restriction reaffirms the importance of integrated management of botrytis in the vineyard, especially in cool, wet growing regions.

To protect Australia’s $1.85 billion (2012) wine exports, the AWRI list satisfies the lowest MRL (maximum residue limits) for any of Australia’s major wine markets. Testing over the previous season was unable to identify a withholding period for boscalid that would meet the MRL requirements of some export markets.

Large wineries and grape purchasers have already informed their growers not to use boscalid.

According to Crop Care Australasia research and development coordinator Doug Wilson, China does not yet have an MRL in place for boscalid, which is the main concern for the coming season. To maintain Australian wine’s clean, green image, AWRI works on zero detection of agrochemicals in wine.

A 2010 GWRDC study placed botrytis and other bunch rots as the second-most important disease, behind powdery mildew. Increased vineyard costs, yield loss and reduced income resulted in an economic impact estimated at $52 million per annum. Considered the most difficult fungal disease to control, particularly if conditions are wet around harvest, botrytis risk is highest in thin-skinned grape varieties with compact bunches in humid canopies carrying high crop loads.

Dr Katherine Evans, Senior Research Fellow at the Tasmanian Institute of Agriculture explains that botrytis spores are almost always in the vineyard, infecting grape tissue via wounds and natural openings. Botrytis development is promoted by the interaction between temperature (optimum 18-21°C) and duration of surface wetness provided by rain, fog, dew or mist.

However, integrated botrytis management aims to manipulate the bunch-zone microclimate for reduced humidity and rapid drying of wet bunches.

The four ‘critical control points’ for managing botrytis include reducing spore load by reducing potential for carryover from one season to the next; reducing flower and fruit infection; limiting the growth of latent infections; and limiting botrytis spread.

She adds that growers do not always have control over the factors promoting each phenomenon such as continuous rain. Dr Evans and her co-researchers have been working on a practical tool for predicting botrytis risk, supporting decisions about fungicide applications and vine canopy management, and planning harvest operations to minimise loss from botrytis.

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