Fire blight susceptibility of select cider apple cultivars

There is increasing interest in growing apple cultivars (Malus domestica Borkh.) of European origin for the production of hard cider in Canada; however, little is known about their susceptibility to fire blight (FB). FB can spread rapidly through apple (and pear) orchards causing extensive tree mortality and economic loss. Twenty-eight promising cider cultivars were evaluated over a 7 year period, and in their seventh year of production they were severely naturally infected by an Erwinia amylovora outbreak causing FB. Herein, we report the bloom and harvest dates and tree mortality that developed largely as secondary shoot blight in the summer of 2021. Overall, the cultivars could be classified according to relative susceptibility to FB, based on percentage tree mortality after 7 years: Enterprise (0%); GoldRush and Porter's Perfection (<20%); Binet Rouge, Kingston Black, Cline Russet, Dabinett, Grimes Golden, Frequin Rouge, Crimson Crisp (R), Cox Orange Pippin, and Muscadet De Dieppe (20%-40%); Calville Blanc d'Hiver, Bramley's Seedling, Yarlington Mill, Michelin, Bulmers Norman, Stoke Red, Golden Russet, Breakwell, Esopus Spitzenberg (50%-90%); Brown Snout, Medaille d'Or, Michelin, Brown's Apple, Sweet Alford, Tydeman Late, Ashmead's Kernel, and Tolman (90%-100%). This study highlights the importance of selecting FB tolerant cider cultivars and following best management orchard practices to reduce the spread and prevent infection, which can be achieved by using FB-resistant rootstock, controlling rootstock suckers, FB prediction models, and limited use of antibiotics, biologicals, and careful nitrogen application to regulate tree vigor.