The Influence of Leaf Removal and Chemical Sprays On Cluster Compactness and Fruit Rot In Riesling Grapevines

Fruit rot causes significant crop loss in many compact-clustered wine grape varieties grown in a cool, humid climate , which has frequent rainfall in the fruit-ripening period. . Grapevines of the compact-clustered Riesling variety, which were grafted on 3309C rootstock and managed with the Scott-Henry training system, were grown at the Michigan State University Southwest Michigan Research and Extension Center near Benton Harbor, Michigan. During the 2008, 2009 and 2010 growing seasons these vines were manipulated in the fruit zone with combinations of leaf removal and single sprays of clove oil, ammonium nitrate, sulfuric acid, acetic acid, sodium hydroxide, ammonium sulfate or copper sulfate at full bloom. Leaf removal was essential to control fruit rot. These chemicals reduced cluster compactness as well as the incidence and severity of fruit rot. There was minimal influence of these vine manipulations on the survival, fruitfulness and yield for the basal two nodes of fruit spurs in the year after treatment. The influence of these strategies for control of fruit rot and yield on whole vines is currently under investigation.