Assessment of bunch thinning as a management technique for Semillon and Shiraz in a hot Australian climate

Abstract

Bunch thinning is a widespread management practice in vineyards and it has been reported to improve grape and wine quality depending on the timing and intensity of its application. This study assessed whether bunch thinning could affect vine performance, grape and wine chemistry and sensory attributes for Shiraz and Semillon in a hot Australian climate.Own rooted Semillon and Shiraz vines planted in 1990 at the Waite Campus of the University of Adelaide were evaluated. For both varieties, bunch thinning was carried out by removing 50 % of bunches at veraison (EL35) for four and two seasons for Semillon and Shiraz, respectively. Vine performance, berry and wine chemistry and berry and wine sensory characteristics were assessed. Results showed a dramatic effect on yield but only minor effects on the other yield components. Berry and wine chemistry were also mostly unaffected by the treatment. Semillon wines from un-thinned vines were preferred, while for Shiraz, bunch thinning improved the wine acceptance by the sensory panel.To support the decision on whether to bunch thin and justify its cost, a significant increase in fruit and wine quality should be expected; however, in this study, only mild effects were found. This study provides the wine industry with a better understanding of the effects of bunch thinning in a hot climate.