Inception and progression of berry shrivel and bunch stem necrosis in the Napa and Sonoma Valleys
Mark N. Krasnow*, Mark A. Matthews, Kenneth A. Shackel
*University of California, Davis; Department of Viticulture and Enology, 1 Shields Avenue, Davis, CA, 95616. [530-752-7185; mkrasnow@gmail.com]
Berry shrivel and bunch stem necrosis are two disorders that afflict vines in the Napa/Sonoma viticultural areas, and symptomatic fruit is usually dropped in the vineyard prior to harvest. Both disorders involve the visible shriveling of the berries during ripening. Clusters displaying berry shrivel have a green, healthy looking rachis. The rachis becomes necrotic in bunch stem necrosis clusters prior to, or at the same time as, visible symptoms appear. In the 2005 season, the timing of the disorders was different: bunch stem necrosis clusters became visibly symptomatic throughout the ripening period, from soon after veraison all the way to harvest. Berry shrivel clusters appeared in the vineyard only in the period of September 3-17. Compositional analyses of the fruit indicate that, while visible symptoms did not appear in berry shrivel fruit until September, the fruit was markedly different in its concentration of sugars, malic acid, and phenolics from non-symptomatic fruit shortly after veraison. Berry shrivel is present and affecting the development of fruit prior to visible symptoms becoming apparent. Compositional data suggests that berry shrivel is not a phenomenon of individual clusters as had been previously thought, but of an entire vine. Healthy appearing clusters from vines that have berry shrivel clusters, or have a history of berry shrivel in previous seasons, are compositionally different than control clusters from vines with no history of BS. The authors would like to thank the American Vineyard Foundation for funding this project.
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