Effect of shoot trimming on yield, fruit maturity, and reserves in Malbec vineyards under a single high-wire trellis system

Abstract

Argentina is the world's fifth largest wine producer and Malbec is its most emblematic variety. Vineyards producing high-quality winegrapes are mainly trellised to vertical shoot-positioned systems. The single high-wire (SHW) system is a highly productive free canopy trellising/training system used in many world wine regions. We evaluated, for the first time in Argentina, the effect of different shoot-trimming levels on leaf area development, yield, grape maturity, and reserve levels of Malbec (clone 598) from SHW-trellised vineyards in Mendoza (Winkler = V). We imposed differenttotal leaf areas (TLA) by shoot-trimming, varying shoot length at full bloom (0.45 m, 0.80 m, or untrimmed) during three growing seasons (2017, 2018, and 2019). We measured yield and fruit composition at harvest and soluble and structural reserves in trunk and canes at leaf fall. Different shoot-trimming levels produced different total leaf area development. The 0.8 m treatment produced 30% less TLA than the untrimmed treatment, while the 0.45 m treatment produced 60% less TLA than the untrimmed treatment, consistently among seasons. The treatments affected yield differentially by season. Overall, the untrimmed treatment had the greatest yields. The 0.80 m treatment, while producing high yields in the second season, was not sustained in the third season and declined to similar yield values as the 0.45 m treatment. This drop in yield could be due to the decrease of starch in the trunk during the second season. On the other hand, grape maturity was greater in the 0.80 m and untrimmed treatments. Our results suggest that the untrimmed treatment produces greater sustained yields over time, with good levels of reserves and grape maturity.