VIEW ARTICLE

Disease Control and Pest Management

Efficacy of Bactericides and Saprophytic Bacteria in Reducing Colonization and Infection of Pear Flowers by Erwinia amylovora. S. V. Thomson, Assistant Professor, Department of Plant Pathology, University of California, Berkeley 94720; M. N. Schroth(2), W. J. Moller(3), and W. O. Reil(4). (2)Professor, Department of Plant Pathology, University of California, Berkeley 94720; (3)(4)Extension Plant Pathologist and Staff Research Associate, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 66:1457-1459. Accepted for publication 4 June 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1457.

Colonization of healthy pear flowers by Erwinia amylovora was reduced as much as fourfold in experimental plots sprayed with bactericides. The bactericides that effectively reduced the number of healthy flowers colonized by E. amylovora also were the most efficacious in reducing the incidence of fire blight. Accordingly, an assay of the percentage of flowers colonized by E. amylovora is an alternative method of determining the efficacy of bactericides, especially when conditions are not conducive for disease development. Fire blight incidence was significantly reduced in a Bartlett pear orchard sprayed eight times during bloom with three saprophytic Pseudomonas spp. and an Erwinia sp. These bacteria, in laboratory studies, multiplied from 10² cells per flower to approximately 10⁵ to 10⁶ cells per flower in 24 hours. The Erwinia sp. produced a bacteriocin lethal to E. amylovora in vitro.