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

Abstract

Two prune (Prunus 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 1- and 2-yr-old shoots declined from November through April