Fire blight is a devastating disease of apple, pear and quince caused by the Gram-negative bacterium Erwinia amylovora. This damaging disease can be prevented with the antibiotic streptomycin, but, as of 2016, streptomycin is no longer permitted for fire blight control in Switzerland. We conducted two experiments in 2015 on alternative methods to control fire blight on pathogen-inoculated, potted two-year old ‘Gala Galaxy’ apple trees in a field site enclosed with mesh. The incidence of fire blight was determined by counting the number of strikes per tree divided by the total number of blossom clusters. Population sizes of E. amylovora were estimated throughout bloom by realtime PCR. A streptomycin application followed by LMA (potassium-aluminum sulfate) treatment showed highest efficacy values and lowest pathogen population sizes on blossoms compared to other tested materials. As streptomycin is not allowed anymore, more research is needed to develop effective alternative plant protection strategies for a sustainable fire blight management in Switzerland.
