Effects of leaf removal on grape cluster architecture and control of Botrytis bunch rot in Sauvignon Blanc grapevines in Southern Brazil

Management practices, such as leaf removal, can affect grape cluster architecture and the microclimate around the cluster, which influences the development of Botrytis bunch rot disease. The timing of leaf removal among five different phenological stages was investigated as a tool for managing grape cluster architecture-related variables and for managing Botrytis bunch rot of Sauvignon Blanc grapevines. A commercial vineyard located in Sao Joaquim municipality, in the highland region of Santa Catarina State, Southern Brazil, was assessed in a randomized complete block design during the 2015 and 2016 growing seasons. The treatments consisted of leaf removal of four basal leaves around clusters at the phenological stages of full bloom, buckshot berries, pea-sized berries, veraison, and 15 days after veraison. At harvest, cluster architecture variables (cluster length, cluster mass, rachis mass, number of berries, berry mass, and cluster compactness index) and Botrytis bunch rot incidence and severity were assessed weekly from the first appearance of symptoms to harvest. Disease progress curves were constructed and compared to several epidemiological parameters. There was no significant effect of the removal of four basal leaves on the cluster architecture-related variables (cluster and berry masses, number of berries, and cluster compactness index); however, reduced the intensity of Botrytis bunch rot. Leaf removal carried out before veraison significantly reduced (P < 0.05) the incidence, severity, AUDIPC, and AUDSPC of Botrytis cinerea in Sauvignon Blanc when compared with those of vines without leaf removal. Early leaf removal at the phenological stages of full bloom, buckshot berries, and pea-sized berries reduced the severity of B. cinerea infection and showed in the phenological stage of full bloom the lowest values for AUDSPC of 199.26 and 171.30 in the 2015 and 2016 growing seasons, respectively. The results of this study suggest that leaf removal carried out before veraison during the phenological stages of full bloom, buckshot berries, or pea-sized berries should be recommended for Sauvignon Blanc cultivar production to reduce Botrytis bunch rot in the highland regions of Santa Catarina State, Southern Brazil.