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Phomopsis Cane and Leaf Spot Disease of Grapevine: Effects of Chemical Treatments on Inoculum Level, Disease Severity, and Yield. Jim D. Cucuzza, Postgraduate Research Plant Pathologist, Department of Plant Pathology, University of California, Davis 95616. Mary Ann Sall, Assistant Professor, Department of Plant Pathology, University of California, Davis 95616. Plant Dis. 66:794-797. Accepted for publication 9 November 1981. Copyright 1982 American Phytopathological Society. DOI: 10.1094/PD-66-794.

A commercial vineyard (Vitis vinifera cv. Tokay) located in Lodi, CA, was used for a 2-yr study of Phomopsis cane and leaf spot disease of grapevines. Fungal activity was monitored by periodically examining the ability of pycnidia to exude spores when hydrated. Pycnidial levels followed a seasonal pattern, with the maximum (15 active pycnidia per square centimeter) being reached just prior to 100% budbreak. Of the three chemicals used to control Phomopsis, dinoseb and sodium arsenite were found to suppress pycnidial activity whereas captan did not. The three chemicals reduced disease severity by different degrees. Pycnidial levels were highly correlated (P ≤ 0.001) with disease and were used as a measured of inoculum. An increase in disease severity was associated with a reduction in the weight of the fruit per vine (r = 0.511, P ≤ 0.05).

Keyword(s): dead arm, epidemiology, Phomopsis viticola.