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Measuring Applied Antagonistic Bacterial Populations for Management of Fire Blight within the State of New York 2006

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Project Leaders: H. Aldwinckle , N. Werner, Department of Plant Pathology, Cornell University, Geneva, NY 14456

Cooperators: D. Breth, Area Extension Educator, Cornell Cooperative Extension; G. Wells, Apple Shed, Newark, NY; M. Maloney, Burnap Farms, Sodus, NY

Abstract: The blossom blight phase of fire blight, caused by the bacterium Erwinia amylovora, is typically managed by applying the antibiotic, streptomycin sulfate, to trees during bloom. Biological control of fire blight can be achieved by applying non-pathogenic bacteria to open flowers that then colonize flower part surfaces and compete with the pathogen for space and nutrients. The objective of this study was to measure the growth of three applied biological control organisms at three orchard locations in New York. We hope to identify safe and effective alternatives to streptomycin because the pathogen is likely to become resistant to streptomycin if this product is used too often. This has already occurred in some western and mid-western states. We detected population levels of the biological control organisms that were slightly lower than those reported in the Pacific Northwest. We also determined that the spread of the biological control organisms increased over time at each location. Application of the bacteria with a handgun sprayer appeared to result in higher populations than when applied with a handheld sprayer. A mixture of antagonists was detected at more than one location, indicating either tank contamination or natural dispersal of the organisms via pollinators. Our results confirmed the ability of these three biological control organisms to colonize and multiply on flowers in New York state. Further studies with larger sample sizes would allow us to make stronger correlations between population levels and incidence of the biological control agents, and their ability to prevent disease.