Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 9/17/2008
Publication Date: 6/1/2008
Citation: Stockwell, V.O., Temple, T., Johnson, K.B., Loper, J.E. 2008. Integrated control of fire blight with bacterial antagonists and oxytetracycline. Phytopathology. 98(6S):151.
Technical Abstract: In the Pacific Northwest of the United States, the antibiotic streptomycin provided excellent control of fire blight until resistant isolates of Erwinia amylovora were prevalent. Oxytetracycline (Mycoshield) is now sprayed as an alternative antibiotic. We found that the duration 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 C9-1) and oxytetracycline in 11 orchard trials inoculated with an antibiotic-sensitive strain of E. amylovora. Two bloom sprays of streptomycin or oxytetracycline reduced the incidence of fire blight of blossom clusters by an average of 73% and 44%, respectively, compared to water-treated controls. A combination of C9-1 and a protease-deficient A506 provided 41% disease control. An integrated treatment, i.e., one application of biological control agents followed by one application of oxytetracycline, provided 59% control. Biological and chemical methods of fire blight suppression were complementary, and consequently, an integrated strategy consisting of a biological control agent sprayed in early and near full-bloom, followed by an oxytetracycline treatment at late bloom, improved disease control with a reduced number of antibiotic applications.