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Leaf Removal for Nonchemical Control of the Summer Bunch Rot Complex of Wine Grapes in the San Joaquin Valley. James J. Stapleton, Statewide Integrated Pest Management Project, University of California Kearney Agricultural Center, 9240 S. Riverbend Ave., Parlier, CA 93648. R. Stanley Grant, E. & J. Gallo Winery Ranches, Livingston, CA 95334. Plant Dis. 76:205-208. Accepted for publication 3 September 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0205.

Field experiments were conducted with several wine grape cultivars during 19881990 near Livingston, California, to determine the effects of leaf removal on summer bunch rot. This cultural practice was found to consistently reduce experimental disease parameters, compared with the nontreated control. Damage due to the summer bunch rot complex (primarily sour rot) was reduced by as much as 69%. A trend toward higher harvestable yields was observed, but differences were rarely significant. Rot reduction after leaf removal was greatest when leaves were pulled from the fruit zone on both sides of cordon-trained vines, but more sunburn also occurred after such treatment. Retaining foliage on the side of the vines facing the afternoon sun reduced the incidence of sunburn but also sometimes reduced the effectiveness of leaf removal in controlling bunch rot. The cost of leaf removal in the San Joaquin Valley may be justified by the benefits of reduced bunch rot, possible enhanced wine characteristics, decreased need for insecticide sprays, and improved pesticide coverage.