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Ecology and Epidemiology

Erwinia amylovora on Fire Blight Canker Surfaces and Blossoms in Relation to Disease Occurrence. S. V. Beer, Assistant Professor, Department of Plant Pathology, Cornell University, Ithaca, N. Y. 14853; D. C. Opgenorth, former Experimentalist, Department of Plant Pathology, Cornell University, Ithaca, N. Y. 14853, Present address of junior author: Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 66:317-322. Accepted for publication 28 August 1975. DOI: 10.1094/Phyto-66-317.

One pear orchard and four apple orchards in Wayne County, New York State, were monitored for the presence of Erwinia amylovora and the occurrence of blossom blight. The pathogen was isolated from holdover canker surfaces in all five orchards by a canker-swabbing technique in which two selective media were utilized. It was detected in blossoms of three of the five orchards 1-3 weeks before blossom infection appeared. The pathogen was not confirmed in blossoms from these orchards in sufficient time to indicate implementation of effective spray applications. Although blossom blight developed in all monitored orchards, more developed in the three orchards in which the pathogen had been detected previously in blossoms. Erwinia amylovora was detected sporadically throughout the season on cankers that had been produced the previous year. Some cankers apparently were active for most of the spring, others were only temporarily active, and E. amylovora was not isolated from the surface of others. Initiation of canker activity appeared to be positively correlated with warm (> 17 C), moist conditions at least 1 day prior to sampling. These studies indicated that holdover cankers may provide inoculum prior to, or without visible evidence of, renewed canker activity, and that E. amylovora may be detected in pome fruit orchards in New York before the development of blossom infection.