Management of bunch rot of Vignoles and Chardonnay grapes with gibberellic acid

• Published in: Phytopathology 2010-06, Vol.100 (6), p.S49-S49
• Main Authors: Hed, B, Ngugi, H K, Travis, J W
• Format: Article
• Language: English
• Subjects: Botrytis cinerea; Vitaceae
• ISSN: 0031-949X

Harvest bunch rot of wine grapes caused by Botrytis cinerea is a perennial problem in the eastern U.S. mat can severely impact wine quality. Previously, we documented a strong relationship between cluster compactness and the incidence and severity of bunch rot on Vignoles grapes. The goal of this study was to investigate the effectiveness of gibberellic acid (GA) applications to loosen clusters as a means for controlling bunch rot on Vignoles and Chardonnay grapes. On Chardonnay, GA applications at 10 or 25 ppm significantly (0.0422 , P , 0.0062) reduced cluster compactness in a 3-year study with bloom applications being more effective than pre-bloom applications. On Vignoles, all bloom applications and the 25 ppm pre-bloom treatments reduced compactness in every year. Depending on the year, GA applications had mixed effects on the incidence and severity of bunch rot on Chardonnay. On Vignoles, combining GA treatments with two fungicide applications resulted in better control of harvest rots than the use of two additional fungicides in 2006 and 2008. Cluster compactness accounted for 52.7% of the variation in the incidence of bunch rot on Chardonnay, between 77.2 and 89.4% on Vignoles, and was negatively correlated (0.731 , r , 0.857; P < 0.0001) with percent spray coverage on berries. In spite of repeated treatment of the same vines for four consecutive years, no negative effects on yield from GA treatments were noted on Vignoles in three of the four years.