Effects of Fruit Zone Leaf Removal on Yield, Fruit Composition, and Fruit Rot Incidence of Chardonnay and White Riesling (Vitis vinifera L.) Grapes

Abstract

Selective leaf removal from grapevine fruit zones was evaluated for three seasons as a means of improving grape quality, especially with respect to fruit rot control. Mature White Riesling (syn. Riesling) and Chardonnay grapevines, grown in two northern Virginia vineyards, were used. Vines were trained to a high (1.8 m above ground), bilateral cordon at one vineyard and a low (1.2 m), bilateral cordon at the other; spur pruning was used at both vineyards. Two treatments, (1) removal of two to four leaves per shoot from around fruit clusters two to three weeks after bloom, or (2) no leaf removal, were compared. Leaf removal increased fruit zone porosity as measured by percentage sunlight penetration, point quadrat analysis, and air-blast spray penetration. Fruit yield components were generally unaffected by leaf removal, although crop per vine and cluster weight were occasionally increased with leaf removal of Riesling. Fruit soluble solids at harvest were reduced slightly in three instances and increased in one, by leaf pulling, while pH and potassium levels remained unaffected. Leaf removal reduced titratable acidity as well as malic acid, although not consistently. The incidence of botrytis and sour bunch rot, as well as the concentrations of rot organism metabolites (glycerol, acetic acid, gluconic acid, and ethanol) in harvested fruit, were reduced with leaf removal of Riesling vines. The chief benefit of leaf removal in this region appeared to be improved bunch rot control with Riesling.