Botrytis Bunch Rot of Grapes: The Influence of Selected Cultural Practices on Infection Under California Conditions. S. D. Savage, Assistant Professor, Colorado State University, Orchard Mesa Experiment Station, Grand Junction 81503. M. A. Sall, Assistant Professor, Department of Plant Pathology, University of California, Davis 95616. Plant Dis. 67:771-774. Accepted for publication 7 December 1982. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-771.

Grape vineyard cultural options including trellis type, midseason hedging, and a fungicide treatment were evaluated for their influence on the development of Botrytis bunch rot. The trials were conducted in an unirrigated coastal valley vineyard (cultivar Chenin blanc) in the 1980 and 1981 growing seasons during which there was no precipitation. Incidence of Botrytis cinerea infection at harvest under drought conditions in 1980 was significantly influenced by trellis type and by fungicide application made at bloom (P<0.05). A commercial-scale harvest of all sprayed portions of the plot was conducted and Botrytis bunch rot damage as assessed by standard state inspection was significantly lower in the “two-wire vertical” trellis (TWV) than in the “crossarm” trellised blocks (XARM, P<0.001). Viticultural parameters of sugar content, pH, total acid, and yield were also evaluated. The hedging treatment led to a significant delay in maturity (sugar content) at the time of commercial harvest (P<0.05). There were no other significant influences of the trellis, hedging, or fungicide treatments on those viticultural parameters. In the 1981 season, the two trellis types were compared and the TWV trellis was associated with significantly lower rot incidence (P<0.05) and also with lower severity expressed as estimated percent rot by weight (P<0.01). Progress of individual infections through the cluster appeared to be slower in the TWV trellis than in the XARM type.