USE OF FRUIT ZONE LEAF REMOVAL WITH VITIS-VINIFERA L CV RIESLING GRAPEVINES .2. EFFECT ON FRUIT COMPOSITION, YIELD, AND OCCURRENCE OF BUNCHROT (BOTRYTIS-CINEREA PERS, FR)

Leaf removal treatments were applied to Vitis vinifera L. cv. Riesling grapevines of varying vigor at two locations in the Niagara Region du ring the 1990 and 1991 seasons to control leaf density in the fruiting zone. Fruit zone leaf removal treatments consisted of a control (no l eaf removal), mechanical leaf removal (MLR) applied either to the west side (WS) or both sides (2S) of the canopy, and hand leaf removal (HL R). 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 l ate treatment dates. The leaf removal treatments exerted no influence on the fruit composition parameters examined with one exception: HLR t reatments had slightly greater sugar concentrations and marginally low er titratable acidity levels than MLR treatments. Yield components wer e 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, respectivel y, than the control. At both vineyards the late leaf removal treatment s had a greater yield per vine than those applied early, and MLR treat ments had a greater yield per vine than HLR treatments. The treatments MLR 2S early and HLR 2S early reduced the incidence and severity of b unch rot (Botrytis cinerea Pers.:Fr.) at KEW vineyards at harvest in 1 990. 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 t he Grape Research Station. Variations in results between years and vin eyards were associated with differences in vine vigor and cluster deve lopment 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.