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Lack of Effect of Stone Fruit Rust on Yield of French Prune Trees and Survival of Urediniospores of the Pathogen on Leaves, Shoots, and Buds. B. TEVIOTDALE, Extension Plant Pathologist, University of California, Davis/Kearney Agricultural Center, Parlier 93648. D. M. HARPER, Staff Research Associate, and T. J. MICHAILIDES, Associate Professor, University of California, Davis/Kearney Agricultural Center, Parlier 93648, and G. S. SIBBETT, Farm Advisor, University of California, Tulare County, Visalia 93721. Plant Dis. 78:141-145. Accepted for publication 22 September 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0141.

Two prune (Primus domestica 'French') orchards, one in Tulare County and one in Yuba County, California, were treated either two or three times in summer with mancozeb or sulfur or left untreated for 3 yr. Fresh and dry fruit weights per tree, number of dry prunes per kilogram, fresh to dry weight ratio, and percent soluble solids were determined each year. Significant differences in yield parameters were few, minor, and inconsistent. Preharvest defoliation did not occur in either orchard in any year, but postharvest leaf loss was faster and leaf infection greater in control and sulfur than in mancozeb treatments. The number of urediniospores on buds declined from November through February, and the number on I- and 2-yr-old shoots declined from November through April. Viable urediniospores were detected on shoots in April of 2 yr and in May of 1 yr and on fallen leaves in May of both years.