Effects on grape and wine quality of bunch thinning of Merlot under Queensland conditions

To date there has been little research on wine grape viticulture in Queensland. While an enormous amount of research data is available for other regions in Australia, findings from elsewhere may not be directly transferable to Queensland conditions. Certain factors make Queensland unique, e.g. a relatively wet growing season often with severe peak heat loads, with most vineyards at high altitude. Even within Queensland techniques may not be directly transferable due to local climatological variations. What is economically efficient in the Granite Belt for example may not be so in the South Burnett and vice versa. Research is needed to assist growers in each region to determine the optimum economic yield for each variety and how best to achieve it.

While there are many varieties grown in Queensland, some have emerged as proven performers and are already widely planted. A series of strategic meetings with members of the Queensland Wine Industry Association identified management of Merlot for quality fruit production as a major issue in need of investigation. Merlot has been shown to perform well in both the Granite Belt and the South Burnett, and is one of the top 5 wine grape varieties planted in Queensland. However, once established Merlot has a tendency to crop heavily and is often bunch thinned with the aim of promoting maturity and increasing berry quality. While it is generally considered that higher wine quality results from lower yield, controlled bunch thinning trials indicate both positive and negative effects, and there is some controversy over this issue. Timing of crop thinning has also been noted as a potentially important factor.