Effects of Timing and Severity of Leaf Removal on Yield and Fruit Composition of Sauvignon blanc Grapevines

¹ Department of Plant Pathology, University of California, Davis, CA 95616-5270.
² Department of Viticulture and Enology, University of California, Davis, CA 95616-5270.

Leaves were removed from mature, quadrilateral-cordon-trained Sauvignon blanc vines at fruit set, four weeks after fruit set, or seven weeks after fruit set. At each time, four levels of leaf removal were employed: Level 0 (control), no leaves removed; Level 1, basal leaves removed; Level 2, basal leaves plus leaves from top of canopy removed; and Level 3, basal leaves plus approximately three consecutive leaves at the top of the south-facing portion of the canopy removed to form a "window." The total soluble solids were significantly higher in fruit from vines with leaves removed. Titratable acidity, malic acid, pH, and juice potassium concentration were all significantly reduced by leaf removal. Increased severity of leaf removal further reduced the pH and potassium concentration in the berry juice at harvest. Yield, cluster number, cluster weight, and berry weight were not significantly affected by the level of leaf removal. Leaf removal significantly increased the photon fluence rate in the fruiting region of the canopy throughout the season. Significant negative correlations were obtained between the photon fluence rate and the pH, malate, and potassium concentration of the berry juice at harvest. A highly significant, positive correlation was found between the levels of malate and potassium in the juice at harvest. Timing of leaf removal did not significantly affect yield components or fruit composition, although earlier leaf removal tended to advance sugar accumulation.

Key words: defoliation, canopy management

Submitted on March 10, 1987