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Ecology and Epidemiology

Epidemiology of Cytospora Canker Caused in Colorado Blue Spruce by Valsa kunzei. L. K. Kamiri, Formerly of the Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824, Current address: Diamond Shamrock Corporation, 1100 Superior Avenue, Cleveland, OH 44114; F. F. Laemmlen, Formerly of the Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824, Current address: Cooperative Extension Service, Imperial County, El Centro, CA 92244. Phytopathology 71:941-947. Accepted for publication 19 January 1981. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-941.

Epidemiological studies of Cytospora canker of Colorado blue spruce (caused by Valsa kunzei [imperfect stage is Cytospora kunzei]) were conducted in 1978 and 1979. Laboratory studies revealed 27 C to be the optimum temperature for conidial germination, germ tube elongation, and linear growth of mycelium. Spore trapping studies were carried out at two locations in Michigan during the 2-yr study period. Ascospores and conidia were both waterborne and airborne. Conidia were detected during periods of wetness throughout the season, but the highest number occurred in the spring. The number of waterborne and airborne conidia always exceeded the number of waterborne and airborne ascospores. The latter were common only in the spring. Discharge of both spore types occurred during both daylight and darkness. Dispersal of airborne ascospores and conidia throughout the season was correlated with mean daily temperature, and hours of 100% relative humidity, leaf wetness, and rainfall. Conidia and ascospores isolated throughout the year were viable.