Severity of fire blight on apple cultivars and strains in Michigan.
During the 1991 growing season, 84 apple cultivars and strains in an experimental planting in Michigan, USA, were evaluated in Jul. and again in Sep. for susceptibility to Erwinia amylovora. All cultivars were infected, with disease severity varying significantly among cultivars: Jonathan, Rome, Idared, Braeburn and Fuji were very susceptible; Golden Delicious, Gala and Jonagold were moderately susceptible; Granny Smith, Empire and McIntosh were intermediate; and Red Delicious and Liberty were moderately resistant. It is concluded that planting of intermediate to moderately resistant rather than susceptible cultivars is the best means of controlling fire blight in areas of Michigan infested by streptomycin-resistant strains of E. amylovora.