Bacterial canker is a significant disease of sweet cherry in Michigan. While disease severity is highly variable between years, symptoms of the disease, especially blossom blast, can significantly reduce yield and requires control measures. Given the current lack of effective and economically viable treatments, bacteriophages are being explored as a potential control. Three bacteriophages were isolated from Michigan cherry orchard soil samples and characterized via in vitro and in situ experiments. This study had two primary objectives in developing effective field treatments: (1) determining if native Michigan bacteriophages are better able to control Pseudomonas syringae pv. syringae isolates from Michigan cherry orchards than a nonspecific commercial product and (2) investigating field treatment modifications designed to reduce bacteriophage UV exposure thereby improving the efficacy of the treatments. The Michigan bacteriophages were determined to lyse significantly more Michigan cherry orchard P. s. pv. syringae isolates than the commercial bacteriophage product in vitro. The field treatments designed to reduce UV exposure had a limited impact on the bacterial populations. However, significant reduction in P. s. pv. syringae populations was observed during a field trial conducted during a period of lower UV radiation, indicating that UV radiation exposure is a primary limiting factor in bacteriophage efficacy. This is supported by the significant decline in bacteriophage populations exposed to UV-C in vitro. These results indicate that if UV exposure is mitigated and the host range is well suited to the environment, bacteriophage could be a useful biocontrol.
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