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Monitoring Erwinia amylovora Populations on Apple in Relation to Disease Incidence. T. B. Sutton, Research Associate, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824, Present address of senior author: Department of Plant Pathology, North Carolina State University, Raleigh 27 607; A. L. Jones, Associate Professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. Phytopathology 65:1009-1012. Accepted for publication 16 April 1975. DOI: 10.1094/Phyto-65-1009.

The Miller-Schroth medium was used for detecting and isolating Erwinia amylovora from infected and from apparently healthy apple tissues. E. amylovora was not detected in samples from 12 apple orchards before fire blight infections were common in the orchards, and, in those orchards where fire blight became severe, not until numerous additional infections were initiated. It is suggested that fire blight outbreaks in Michigan result from the rapid development of temporary epiphytic populations of E. amylovora following infrequent, but widespread, dissemination. Possible modifications of the sampling technique and the need for a predictive model are discussed.