In this project, researchers wanted to evaluate the effects of late pruning and increased temperatures on the development and fruit composition of Shiraz.
Shiraz vines in the Barossa valley were used for the three year trial. One group of vines were exposed to elevated temperatures and the other to ambient temperatures. Within each temperature regime, three pruning strategies were implemented:
Control: Conventional winter pruning
- Budbreak: Vines pruned at budbreak
- 2-3 leaves: Vines pruned once 2-3 leaves unfolded
Late pruning delayed phenology from budbreak to veraison and delayed harvest in four out of six cases. The largest delay was 17 days in unheated vines pruned when two to three leaves had emerged.
- Late pruning delayed the harvest by shifting the onset and rate of ripening.
- Heating advanced phenology at flowering and veraison but did not hasten ripening from veraison to harvest. Heating had only a minor effect on winter pruned vines.
- Pruning weights were unaffected by late pruning and were increased by heating.
- Yield was increased in only one season by late pruning and heating, but yield remained unchanged for the pooled three-year data.
- There were interactive effects of heating and pruning on pH and TA depending on whether late-pruned vines were unheated or heated.
- Late pruning maintained the anthocyanin-to-sugar ratio, which decreased with heating in two seasons.
- There was an interaction between the timing of pruning and heating, whereby late pruning enhanced the berry tannin-to-sugar ratio in heated but not in unheated control vines.
- The delay in ripening (TSS) of late-pruned vines was greater when seasons were warmer close to harvest. Heating did not affect pH over the three seasons.
- In addition to heating effects on reducing berry colour, the anthocyanin-to-TSS ratio was negatively correlated with yield in 2013 to 2014, but not in 2014 to 2015.
Significance of the study
As temperatures are rising, harvests are becoming more compressed. Strategies such as late pruning need to be investigated to determine if it can be implemented to mitigate the effect of warmer summers. This study concluded that late pruning can effectively delay development of Shiraz berries under conditions found in the Barossa Valley, while having neutral effects on yield. Therefore, late pruning may help to counteract some of the effects of warming on oenologically important berry properties.
Martin Moran, Paul Petrie and Victor Sadras. Effects of Late Pruning and Elevated Temperature on Phenology, Yield Components, and Berry Traits in Shiraz. Am. J. Enol. Vitic. 70:1 (2019), p9-18
Link to article: http://www.ajevonline.org/content/70/1/9