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ABSTRACT Mature ‘Vidal blanc’ and ‘Chardonnay’ (Vitis sp.) grapevines were cluster thinned at different times to determine the influence on vine growth and fruiting. Cluster thinning to one cluster per shoot decreased yield and increased juice soluble solids concentrations. In one three-year study, cane node length (4,8 or 12 nodes) was imposed to develop different canopy densities. There was no interaction between cluster thinning time and cane node length. Clusters produced on longer canes had reduced cluster and berry weight, but cane length had no effect on juice components. A comparison of cluster thinning times from bloom to near veraison on ‘Vidal blanc’ showed the increase in cluster weight and juice pH became greater as time of cluster thinning was delayed. Berry weight reached a maximum when vines were cluster thinned two weeks after bloom. Juice total soluble solids of both ‘Vidal blanc’ and ‘Chardonnay’ was increased equally by all times of cluster thinning. There was no effect of cluster thinning on pruning weight, the distribution or origin of shoots, or leaf mineral levels. These studies show that positive effects on fruit quality occur by cluster thinning wine grapes over the growing season prior to veraison.