Postveraison Leaf Removal Does Not Consistently Delay Ripening in Semillon and Shiraz in a Hot Australian Climate

Abstract

Grapegrowing areas worldwide are experiencing earlier and compressed phenology because of higher temperatures, which has led to excessive sugar accumulation in grapes. This is associated with negative effects on grape and wine quality and higher alcohol in wines. Recent research has shown that early, climate-related ripening can be ameliorated by late leaf removal above the cluster zone. This practice was found to delay sugar accumulation in the berries by up to two weeks without affecting other berry chemistry parameters. Therefore, in this study, postveraison leaf removal was investigated as a canopy management technique to delay ripening in Semillon and Shiraz in a hot climate in Australia. Yield and yield components, canopy size, berry and wine chemistry, and sensory attributes were measured over four seasons for Semillon and two seasons for Shiraz. The results showed no effect of the proposed technique on delaying ripening in the first year of application for both varieties. However, on the second year of application, a delay in ripening of 10 days in Semillon and 20 days in Shiraz was observed. In Semillon, postveraison leaf removal did not delay ripening on the fourth year of application. No differences were observed in berry chemistry and sensory attributes in Semillon. In Shiraz, wines obtained from defoliated vines in the second season were different from control wines, and were characterized by attributes consistent with overripe berries such as dry fruit and jammy aromas and flavors. The results from this study showed that this technique was not effective in consistently delaying ripening in Semillon and Shiraz in a hot Australian climate.