Master of Science, The Ohio State University, 2012, Horticulture and Crop Science

Several winegrapes grown in cool climates, including Vitis vinifera Cabernet Franc and Vitis sp. Chambourcin, benefit from crop reduction. The practice promotes timely fruit maturation and can improve fruit quality. Balanced pruning and cluster thinning are the cultural practices used to attain the desired crop load. However, crop reduction by cluster thinning is labor intensive, costly and typically not mechanized for winegrapes. In this study, the practice of early season leaf removal by hand and with a mechanized leaf remover is proposed as an alternate tool to reduce crop level, thereby optimizing crop load and fruit quality. The objectives were to determine the effects of the timing of leaf removal (pre-bloom, bloom, or fruitset) on yield components, crop load, fruit quality, and cold hardiness in Chambourcin and to 2) determine the effects of manual versus mechanical leaf removal at different phenological stages on yield components, growth, crop load, and fruit quality in Cabernet Franc. In Chambourcin, leaf removal at pre-bloom in 2010 and bloom in 2010 and 2011 reduced yield as compared to defoliation at fruitset and control (no removal). Early season leaf removal reduced crop load (Ravaz index) in both years. Defoliation at bloom increased bud lignification in both years and reduced bud injury in fall of 2010. Defoliation at pre-bloom reduced bud injury in winter in one of two years. In Cabernet Franc, manual leaf removal at pre-bloom and mechanical leaf removal at bloom reduced yield. Leaf removal had no negative effects on pH, titratable acidity, soluble solids, or total phenolics in either cultivar in either year. Early season leaf removal can be used to control yield without negatively impacting growth, cluster compactness, disease incidence, fruit composition, or lignification. It is concluded that early season leaf removal is a viable alternative to cluster thinning as a method of yield reduction in Chambourcin. Early season mechanical leaf removal is (open full item for complete abstract)

Committee: Imed Dami Dr (Advisor); Douglas Doohan Dr (Committee Member); Joseph Scheerens Dr (Committee Member); Michael Ellis Dr (Committee Member) Subjects: Agriculture; Horticulture