Factors Determining the Relative Number of Ascospores Released by Eutypa armeniacae in California. C. H. Petzoldt, Graduate Research Assistant, Department of Plant Pathology, University of California, Davis 95616. M. A. Sall, Assistant Professor, and W. J. Moller (deceased), Extension Plant Pathologist, Department of Plant Pathology, University of California, Davis 95616. Plant Dis. 67:857-860. Accepted for publication 4 January 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-857.

Based on data taken from a Hirst-Burkard spore trap surrounded by a ring source of inoculum, two parameters have been identified as important for determining the number of ascospores discharged in a single release period of Eutypa armeniacae. These are 1) duration of surface free moisture and 2) days from previous release. An "exhaustion" phenomenon was observed during discharge episodes of long duration. Release was triggered either by rainfall or irrigation and ascospores were not released in significant numbers in summer in California despite wetness conditions that caused release at other times of the year.

Keyword(s): apricots, grapevines.