INTEGRATED CONTROL OF FIRE BLIGHT WITH ANTAGONISTS AND OXYTETRACYCLINE

In the Northwest United States, the antibiotic streptomycin provided excellent control of fire blight until resistant isolates of the pathogen arose. Oxytetracycline (Mycoshield) is now sprayed as an alternative antibiotic. We found that the durability of inhibitory activity of oxytetracycline is similar to that of streptomycin, but oxytetracycline is considerably less effective than streptomycin when the antibiotics are targeted toward sensitive strains. In an effort to improve disease control, we evaluated combinations of biological control agents (Pseudomonas fluorescens A506 or Pantoea agglomerans C9-1S) and oxytetracycline in eight orchard trials inoculated with an antibiotic-sensitive strain of Erwinia amylovora. Two bloom sprays of streptomycin or oxytetracycline reduced the disease incidence by an average of 76% and 42%, respectively, compared to water-treated controls. A combination of C9-1 and a protease-deficient A506 provided 42% disease control. An integrated treatment, i.e., a spray of biological control agents followed by one application of oxytetracycline provided 57% control. Biological and chemical methods of fire blight suppression appear to be complementary, and consequently, an integrated strategy consisting of a biological control agent sprayed in early and near full-bloom, followed by oxytetracycline treatment at late bloom improved disease control with a reduced number of antibiotic applications.