Kevin Usher,* Pat Bowen, Tom Lowery, Carl Bogdanoff, and Jose Urbez-Torres
*Summerland Research and Development Centre, 4200 Highway 97, P.O. Box 5000, Summerland, BC, V0H 1Z0, Canada (kevin.usher@agr.gc.ca)

Leaf removal is a canopy management practice that can improve wine quality and influence the physical attributes of clusters. Pre-bloom leaf removal affects cluster size, compactness, and yield while improving quality, while leaf removal at fruit set or veraison does not alter physical attributes, but does impact quality. Phenolic compounds important to wine quality are significantly affected by leaf removal. The effects of seven leaf removal timing and intensity treatments on anthocyanins, procyanidins, and quercetins were evaluated over three years in Syrah grapes grown in Osoyoos, British Columbia. Pre-bloom leaf removal was applied by removing either four or six basal leaves at two weeks prior to bloom. Fruit set leaf removal was applied by removing 50% or 100% of leaves in the fruiting zone, and similarly for the veraison treatment, 50% or 100% of leaves in the fruiting zone were removed. HPLC analysis of phenolic components in grape skin and seeds included the quercetin glycosides, anthocyanins, catechin, and epicatechin. The pre-bloom treatments reduced catechin and epicatechin by up to 40% in both seeds and skin, while the other treatments also resulted in some reduction. Quercetin-3-glucoside and quercetin-3-glucuronide increased with most treatments and by up to 70% in the six leaf pre-bloom treatment. Total anthocyanins increased with pre-bloom leaf removal in two out of three years, but in fruit set and veraison treatments, they decreased or were not significantly different. Non-acylated anthocyanins were affected most by leaf removal, while the acetylglucosides and cinnamoyl derivatives were not different. The results show that timing and intensity of leaf removal can alter fruit quality through changes in phenolic composition.

Funding Support: British Columbia Wine Grape Council Agriculture and Agri-Food Canada