The Influence of Girdling and Gibberellic Acid Application at Fruitset on Ruby Seedless and Thompson Seedless Grapes

¹ Department of Viticulture and Enology, University of California, Davis, CA 95616
² Department of Viticulture and Enology, University of California, Davis, and Kearney Agricultural Center, 93240 S. Riverbend Ave., Parlier, CA 93648

The effects of girdling and gibberellic acid (GA) on berry weight, soluble solids concentration, and yield of Ruby Seedless and Thompson Seedless table grapes were determined. Treatments included trunk girdling and GA application (40 mg/L) to entire vines, shoots only, or clusters only at fruitset. Berry growth and development were monitored several times between fruitset and harvest. Girdling increased berry weight approximately 0.8 g for both cultivars. GA applied to entire vines or to clusters only significantly (p < 0.01) increased berry weight of Ruby Seedless vines by 0.26 and 0.56 g over the control. Girdling reduced the soluble solids concentration at harvest by 0.8°Brix. Soluble solids of GA vine-, shoot-, and cluster-sprayed fruit were equal to or above the control. Vine yields were significantly (p < 0.01) increased by girdling. The number of clusters on Ruby Seedless grapevines were reduced to 54 per vine the following spring on treatments that had GA sprayed on the shoots, as compared to 82 clusters per vine for the control. Results demonstrated that the berry weight of Ruby Seedless vines could be increased by girdling and GA treatments at fruitset. Submitted on May 19, 1986