Late pruning to delay maturity and preserve wine identity in Barossa Shiraz

Abstract

Warming is shifting vine phenology, compressing harvests, and altering the balance of fruit traits relevant to wine. The aim of this thesis was to test late pruning as a tool to delay maturity of Shiraz in the Barossa Valley of Australia, and its impact on vine yield, and wine chemical and sensory attributes. Pruning at three phenological stages were compared: winter (control), budburst and 2-3 leaves emerged. Two trials were established. First, three pruning treatments were carried out during four consecutive seasons on the same vines, to evaluate carry-over effects. Second, two thermal regimes (heating with open-top chambers vs unheated control) was combined with three pruning times during three seasons. In general, late pruning treatments delayed maturity with neutral or positive effects for yield and berry traits without carry-over effects on phenology, yield, leaf area and berry traits. Further, late pruning shifted the onset of berry anthocyanin in relation to sugars and increased the anthocyanin to sugar ratio, improved wine phenolics and altered sensory attributes. In a context of warming, delaying pruning until 2-3 leaves have emerged can effectively spread the harvest and partially restore anthocyanin : sugar ratio, improve wine phenolics and preserve wine sensory attributes with no yield penalties.