Cluster thinning as a tool to hasten ripening of wine grapes in the Okanagan Valley, British Columbia.

Hannam, K.D., Neilsen, G.H., Neilsen, D., and Bowen, P.A. (2015). "Cluster thinning as a tool to hasten ripening of wine grapes in the Okanagan Valley, British Columbia.", Canadian Journal of Plant Science, 95(1), pp. 103-113. doi : 10.4141/cjps2013-397  Access to full text

Abstract

Achieving fruit maturity can be a challenge on some Okanagan vineyards in some years. Cluster thinning is widely used to hasten ripening, but may not be effective on sites with balanced crop loads. In a Merlot vineyard in Summerland, BC, the effects of cluster thinning on juice soluble solids (an indicator of fruit maturity), yield and vine growth were examined between 2008 and 2011 across a range of treatments that manipulated the frequency and quantity of applied irrigation water. Cluster thinning increased juice soluble solids in 2 out of 3 study years and consistently increased cluster weights, but had few effects on juice pH, titratable acidity or yield. In 2 of 3 yr, correlation analyses showed that cluster thinning was most effective at improving the maturity of fruit with low soluble solids. Irrigation treatments did not have a consistent effect on juice composition but year-to-year variability was significant. Response ratios calculated from values reported in the literature show that cluster thinning in this region causes small but inconsistent improvements in juice soluble solids across a range of crop loads.

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