Overview
This report is a background knowledge source on predicting and managing Botrytis bunch rot in cool climate vineyards. Trials in southern Tasmania and the Yarra Valley, combined with New Zealand data, calibrated a prototype Botrytis Decision Support Model. It forecasts seasonal risk and predicts harvest severity from weather, management and monitoring data. A fungicide applied between pea-sized berries and pre-bunch closure generally reduced botrytis at harvest substantially. Bunch thinning and bunch trash removal did not help, and leaf removal helped only where canopies were dense. A whole-block trial showed spray responses varied with grapevine vigour.
Botrytis bunch rot, caused by Botrytis cinerea, causes significant loss of yield and quality in wine grapes grown in cool, temperate regions of the world. In Australia and New Zealand, synthetic fungicides continue to be used widely for protection of grape flowers and fruit when they are susceptible to infection by B. cinerea; however, there is increasing restriction on botryticides available for protection during berry ripening because of market specifications for low or no fungicide residues in wine. Dry seasons and low grape prices in recent years have seen spray programs reduced (less water and diesel) and canopy management minimised (less labour). When conditions then return to being highly favourable for disease, growers can suffer economic losses if they have not adjusted their inputs accordingly. Conversely, the same intensive, season-long spray program may be used regardless of actual botrytis risk. Prior to this project, The New Zealand Institute of Plant and Food Research Limited (P&FR, formerly HortResearch) had been developing a model that incorporated weather related botrytis risk identified in existing models, with pathogen inoculum and vine factors integrated for determining overall botrytis risk.
This report describes results from 17 replicated, small-plot trials conducted in southern Tasmania and the Yarra Valley of Victoria in the period 2006-2009 for testing various fungicide programs and canopy management techniques for their impact on botrytis severity at harvest. Data from these trials and those from another 34 site-years conducted by P&FR in New Zealand in the period 2001-2009 were used to quantify botrytis risk relationships in relation to weather, vine factors and fungicide use. These risk relationships were integrated into the prototype Botrytis Decision Support Model (BDSM) with data from the final growing season (2008/09) used to calibrate the prototype model using different fungicide timings.
Abstract
Botrytis bunch rot, caused by Botrytis cinerea, continues to cause large seasonal variability in grape production and wine quality. This project identified pathogen, vine and weather factors that can be practically monitored during the season for predicting botrytis risk.
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