Experiments in New Zealand have shown promising results with the post flowering use of harvesters to reduce bunch rot incidence and manipulate bunch architecture. To assess whether these results can be achieved in Western Australia, harvester experiments were conducted on five white varieties across three different growing areas. No statistically significant findings, across a number of bunch compaction parameters and bunch rot incidence, were found for all harvester treatments. Weather conditions during the 2020 vintage in WA were optimal for grape growing, being the major influence behind these findings. Further investigations are required during years where less optimal weather conditions occur.
Bunch rots are a significant cost to the profitability of Western Australian wine producers due to direct losses of fruit, harvest downgrades and the costs associated with their control. Further pressure has occurred with the recent loss of iprodione from the market and export markets moving towards a requirement for fewer pesticide applications. Successful use of a post flowering harvester treatment would provide a pesticide free approach to bunch rot management.
Reducing bunch compaction is considered the holy grail of bunch rot management but this is not easy to achieve on mature vineyards. Use of harvesters to remove bunch trash after flowering has minimised bunch rots under New Zealand conditions and reduced compaction. It is unknown whether the same result will occur in WA due to differences in climatic conditions.
With the assistance of three commercial vineyards in the Margaret River and Pemberton regions this project is a preliminary investigation into the potential of post flowering applications of harvesters to reduce bunch rot in WA. Overall, the results did not highlight any significant differences in the harvester treatments and the non-harvester controls, as the weather during the 2020 vintage in south-west WA was not conducive for disease development. The fact that there were no differences recorded means there are no negative impacts on wine quality from the use of the harvesters at this growth stage. Further investigations are required during years where the weather is favourable for disease development, to provide a full understanding as to the impact of this control technique.