Exploring grapevine canopy management: effects of removing main leaves or lateral shoots before flowering

Abstract

Over the course of a six-year trial, we investigated the physiological response of the Swiss white cultivar Vitis vinifera Petite Arvine, rich in varietal thiols, to the following canopy removal treatments from the cluster area, i.e. from the shoot base to the sixth leaf of each shoot: A) lateral shoots only, B) lateral shoots + 50 % main leaves, C) lateral shoots + 100 % main leaves or D) main leaves only. All leaf removal (LR) treatments were performed at the pre-flowering stage. Intensive pre-flowering removal of both lateral shoots + 100 % main leaves from the cluster area (C) strongly reduced yield potential (‒47 % on average) and tended to reduce the concentration of 3-mercaptohexanol precursors (Cys-3MH) in the must (‒21 %; p-value < 0.10). The effect of LR on berry set and must composition was modulated by removing fewer main leaves (‒24 % in yield potential and ‒6 % in Cys-3MH concentration). Climate conditions primarily influenced yield and grape composition. Main leaves and lateral shoots played different physiological roles: removal of main leaves only (D) resulted in a larger leaf area (+15 %) due to the development of lateral shoots in the cluster area and a lower yield potential (‒12 %) due to fewer berries per cluster when compared one-to-one with removal of lateral shoots only (A). In the must at harvest, treatment D had higher concentrations of malic acid (+12 %), yeast-assimilable nitrogen (+10 %) and glutathione (+8 %), but there were no significant trends for TSS, pH, Cys-3MH or Folin index. The overall effects of pre-flowering LR on wine composition were negligible in the context of this trial. The study highlighted the different physiological roles of the main leaves and lateral shoots, suggesting that pre-flowering leaf removal should be used cautiously, taking into account the plant’s resilience to environmental conditions. This research is part of a broader project on grapevine canopy management in temperate climates in Switzerland.