Leaf Removal Effects on Cabernet franc and Petit Verdot: II. Grape Carotenoids, Phenolics, and Wine Sensory Analysis

Abstract

The rationale for fruit zone leaf thinning in a humid environment is often driven more by the need for disease management than by anticipated improvements in fruit composition. Fruit zone management is often applied uniformly over climatically diverse regions, with little regard for interaction with ambient temperature or radiation. We evaluated how the timing and magnitude of fruit zone leaf and lateral removal altered fruit composition and wine consumer preference of Cabernet franc and Petit Verdot, with the underlying premise that current fruit zone management recommendations (one to two leaf layers) may be overly conservative in the humid, eastern United States. Three post-fruit set leaf/lateral shoot removal treatments (no removal [NO], removal from opposite the basal primary cluster and the node directly above [MED], and removal from the node directly above the distal primary cluster down to the cordon [HIGH]) and one pre-bloom leaf/lateral shoot removal treatment (removal from the six primary basal nodes [P-B]) were evaluated. P-B more consistently increased total berry phenolics in Petit Verdot than in Cabernet franc, while total berry anthocyanins were unaffected. Carotenoids were quantified due to their importance as aroma precursors. When compared to NO and MED, HIGH and P-B treatments tended to increase carotenoid accumulation more in the preveraison period than in the postveraison period. HIGH and P-B treatments also tended to increase carotenoid degradation more in the postveraison period, particularly for zeaxanthin. Wines made with fruit from P-B plots were ranked higher in color intensity compared to wines made with fruit from MED plots. Fruit zone leaf removal modestly improved fruit composition and wine quality potential, and created a microclimate less conducive to fungal diseases.