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The use of prohexadione calcium and a systemic acquired resistance inducer to manage fire blight without antibiotics

Anna Wallis: PPPMB Cornell University

<div>Fire blight, a bacterial disease of pome fruit caused by <em>Erwinia amylovora</em>, is one of the most important diseases affecting commercial apple production. It has become increasingly problematic with the widespread adoption of high density orchards and the warming climate. Antibiotics are the most effective management tool, but raise concern due to the potential for antibiotic resistance. Alternatives include systemic acquired resistance (SAR) inducers, which prime host defense responses, and prohexadione calcium (PhCa), a plant growth regulator that inhibits internal invasion of the pathogen. We evaluated the SAR inducer Regalia and various PhCa programs compared to untreated controls and standard antibiotic programs for their effects on blossom and shoot blight, crop load, and shoot growth for two years. Antibiotics provided excellent control (<5% blossom & shoot blight incidence) compared to control trees. Single applications of the SAR inducer and PhCa at pink provided good control alone (<30%), but control improved when treated with copper prior to inoculation (<10%). Tree growth and productivity were not affected by the end of the season. Multiple, low rate PhCa applications provided excellent shoot blight control, but prolonged programs slightly impeded shoot growth. Future work should further refine PhCa programs and evaluate effects on plant growth in the absence of <em>E. amylovora</em>.</div>