Submitted to: Fire Blight International Workshop
Publication Type: Abstract Only
Publication Acceptance Date: 6/5/2007
Publication Date: 8/12/2007
Citation: Stockwell, V., Temple, T., Johnson, K., Loper, J.E. 2007. Integrated Control of Fire Blight. Fire Blight International Workshop. Interpretive Summary:
Technical Abstract: 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, but it is considerably less effective than streptomycin when the latter was targeted toward sensitive strains. Biological control agents, Pseudomonas fluorescens A506 or Pantoea agglomerans C9-1, also reduce the incidence of fire blight, generally to levels comparable to oxytetracycline. In an effort to improve disease control, we evaluated combinations of biological control agents and oxytetracycline in seven orchard trials inoculated with an antibiotic-sensitive strain of Erwinia amylovora. Biological control agents were killed when tank-mixed with oxytetracycline, but tolerated this antibiotic when sprayed onto flowers on which the agents had become established. Two bloom sprays of streptomycin reduced the disease incidence by an average of 77% compared to water-treated controls. Oxytetracycline reduced disease incidence by 47%. A506 alone reduced the disease incidence by 19%, whereas 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 an application of oxytetracycline provided 55% (A506 alone) and 62% (mixed agents) control. Biological and chemical methods of fire blight suppression appear to be complimentary, and consequently, an integrated strategy consisting of a biological control agent sprayed early in bloom, followed by oxytetracycline treatment at mid- to late bloom provides improved disease control with a reduced number of antibiotic applications.