Evaluation of Dormant-Stage Inoculum Sanitation as a Component of a Fire Blight Management Program for Fresh-Market Bartlett Pear

From 2010 to 2013, the efficacy of copper-based inoculum sanitation as a component of fire blight management programs was evaluated in commercial pear orchards located in northern California. Forty-one 4-ha sections of orchard were split into two equal-sized plots, with the orchardist applying horticultural oil alone to one plot and horticultural oil plus a fixed copper bactericide to the other plot. These treatments were timed to begin just prior to and finish at the "green tip" phenological stage, which occurs about 5 weeks before full bloom. During bloom, flower samples were collected from the plots and subjected to a loop-mediated isothermal DNA amplification (LAMP) assay for specific detection of Erwinia amylovora. Overall, epiphytic populations of E. amylovora on flowers were detected rarely at midbloom (6% of samples) but commonly at petal fall (44% of samples). In three of four seasons, E. amylovora detection in flower samples at a given bloom stage was significantly suppressed in copper-plus-oil-treated plots compared with oil-only plots. All orchards also received antibiotic treatments during the bloom period and, perhaps as a consequence, the development of fire blight was sporadic and not affected significantly by the copper treatment in any season. The pathogen detection data indicate that copper sanitation may add value to a fire blight management program by delaying the increase of epiphytic populations of E. amylovora in flowers to the late stages of the bloom period, at which time the number of susceptible flowers declines rapidly.