Use of Fruit Zone Leaf Removal With Vitis vinifera L. cv. Riesling Grapevines. II. Effect on Fruit Composition, Yield, and Occurrence of Bunch Rot (Botrytis cinerea Pers.:Fr.)

¹ Dept. of Horticultural Science, University of Guelph, Guelph, Ont. N1G 2W1, Canada
² Horticultural Research Institute of Ontario, P.O. Box 7000, Vineland Station, Ont. L0R 2E0, Canada.

Leaf removal treatments were applied to Vitis vinifera L. cv. Riesling grapevines of varying vigor at two locations in the Niagara Region during the 1990 and 1991 seasons to control leaf density in the fruiting zone. Fruit zone leaf removal treatments consisted of a control (no leaf removal), mechanical leaf removal (MLR) applied either to the west side (WS) or both sides (2S) of the canopy, and hand leaf removal (HLR). Treatments were applied when the berries had reached pea size (i.e., early), just prior to veraison (i.e., late), or at both early and late treatment dates. The leaf removal treatments exerted no influence on the fruit composition parameters examined with one exception: HLR treatments had slightly greater sugar concentrations and marginally lower titratable acidity levels than MLR treatments. Yield components were affected by leaf removal at KEW vineyards, with MLR 2S late having a 19.3% and 11.2% greater crop per vine and cluster weight, respectively, than the control. At both vineyards the late leaf removal treatments had a greater yield per vine than those applied early, and MLR treatments had a greater yield per vine than HLR treatments. The treatments MLR 2S early and HLR 2S early reduced the incidence and severity of bunch rot (Botrytis cinerea Pers.:Fr.) at KEW vineyards at harvest in 1990. At harvest in 1991, MLR 2S early, MLR 2S early and late, and HLR 2S early and late reduced the incidence and severity of bunch rot at the Grape Research Station. Variations in results between years and vineyards were associated with differences in vine vigor and cluster development prior to the application of the first leaf removal. Therefore, the use of leaf removal in the Canadian Niagara region with Riesling grapes results in the improvements of yield components and a reduction in the incidence and severity of bunch rot.

Key words: leaf removal, Riesling grapevines, yield, fruit composition, Botrytis cinerea

Submitted on January 8, 1993

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