Comparison of Fungicide, Leaf Removal and Gibberellic Acid on Development of Grape Clusters and Botrytis Bunch Rot of ‘Vignoles’ and ‘Pinot Gris’

Abstract

Abstract 'Vignoles' and ‘Pinot Gris’ grapes, which have compact clusters, were treated with iprodione (Rovral) fungicide, selective leaf removal and gibberellic acid (GA3) over several years to determine the influence on Botrytis bunch rot infection, cluster development, yield and quality. Treatment of individual clusters with GA3 tended to increase cluster weight and length, and decrease berries with rot, but differences were not always significant. The fungicide iprodione provided good control of Botrytis bunch rot and leaf removal reduced incidence approximately 50% of that achieved by the fungicide. Most years yield was not affected by GA3 application at bloom, but in 1999 GA3 reduced the yield of ‘Vignoles’ 37% and ‘Pinot Gris’ 40%. None of the treatments affected juice quality. Changing cluster architecture with GA3 or exposing clusters by leaf removal were sufficient alone to control bunch rot on susceptible cultivars under humid Midwest conditions, and should be integrated with a fungicide program.