Effect of vineyard management of Cabernet Sauvignon (Vitis vinifera L.) grape glycosides

Quantification of grape glycosides has been suggested as an objective index of grape quality. Two studies were undertaken to observe the influence of vineyard management on grape glycosides. In the first study, three crop levels from mature Cabernet Sauvignon (Vitis vinifera L.) vines grown in eastern Virginia were evaluated for their influence on grape glycosides, expressed as red-free glycosyl glucose (GG). Crop levels averaged 3.2, 5.1, and 6.4 kg/vine resulting in leaf area to fruit weight ratios (cm²/g) of 34.4, 27.0 and 19.2, respectively. Red-free GG was greatest in juice from fruit of the low treatment at four of seven sampling dates, including harvest. Phenolic glycosides were found to comprise as much as half of the total GG value. In a second study, shoot thinning, mechanical and hand fruit zone leaf removal of mature Cabernet Sauvignon grapevines were evaluated for their influence on red-free GG. Two shoot densities were examined, each with no leaf removal (No LR), mechanical leaf removal (M LR) or mechanical plus hand leaf removal (M+H LR) imposed five weeks post-bloom. Red-free GG was increased by leaf removal of shoot thinned vines and was greatest with mechanical plus hand leaf removal.