Consequences of late leaf removal on the upper part of the canopy on grapevine water status and grape characteristics of Vitis vinifera L. 'Pinot noir'

One of the main challenges of growing grapevines in a warmer climate is that grape sugar accumulation gets faster and soluble solids content at harvest exceeds the target chosen by grape growers, specifically for wine production, where alcohol level is a key component of wine quality. When grapevines are cultivated on a trellis with vertical shoot positioning (VSP), leaf removal on the upper part of the canopy after veraison makes it possible to delay and limit sugar quantity in grapes. The impacts of this technique have been assessed in Burgundy (France), during vintages 2020 and 2021, on Vitis vinifera 'Pinot noir' planted in 2015. Three treatments have been compared with respect to a control: a severe leaf removal (2/3 of the upper foliage eliminated) applied before veraison (25 days approximately before mid-veraison), a light leaf-removal (1/3 of the upper foliage eliminated) applied before veraison and a severe leaf-removal applied 5 to 10 days after mid-veraison (late veraison treatment). Analyses on mature grapes show a significant decrease in the sugar content when a severe leaf removal was performed during vintage 2021. The water status of the vines during the ripening period of the grapes, assessed using delta C-13 (carbon isotopic discrimination) was significantly different between the treatments. The severe leaf removal significantly reduced grapevine water deficit, especially if it is applied before veraison. These results suggest that the leaf removal of the upper part of the canopy may be a relevant technique to adapt grapevine cultivation according to the heat and dryness of the current vegetative season.