Date of Award


Degree Name

MS in Agriculture - Crop Science


Horticulture and Crop Science


W. Keith Patterson


Syrah is an important wine grape in California but is potentially difficult to manage in the vineyard due to its excessive vigor. Vigorous grapevines require more labor for canopy management and tend to create excess shade, decreasing fruit quality. Winter pruning level, shoot thinning and leaf removal influence the overall density of the canopy and the subsequent degree of shade in the fruit zone. An experiment was conducted to assess the effects of two pruning levels with three degrees of labor-intensive canopy management techniques on berry maturation rate and harvest berry parameters for two growing seasons. In 2008, repeated measures analysis showed no significant effects of severe pruning, shoot thinning or both sides leaf removal on maturation rate of performance indicators. At harvest 2008, severe pruning caused a decrease in yield/meter trellis and Ravaz index. In 2009, repeated measures analysis showed significant effects of severe pruning increasing brix, pH and sugar to acid ratio while shoot thinning and both sides leaf removal had no significant effects on maturation rate of performance indicators. At harvest 2009, severe pruning increased brix, pH, tannin, anthocyanins, phenolics, color density, potassium, amino acid % of yeast assimilable nitrogen (YAN), and the following ratios: sugar/acid, amino acid/ammonium, tannin/anthocyanins and malic/tartaric acid. Additionally, severe pruning decreased tartaric acid, yield/meter trellis, ammonium % of YAN and Ravaz index. The findings presented in this thesis suggest that severe pruning could be used as a tool in viticultural areas with short growing seasons because of the increased ripening speed observed. However, because severe pruning generally increases berry size which is negative for vinification, it should be studied further with irrigation and management practices that decrease berry size.

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