Fungicide efficacy trials for the control of powdery mildew (Podosphaera cerasi) on sweet cherry trees (Prunus avium)

Powdery mildew is a detrimental foliar disease of sweet cherry trees. The disease is predominantly managed by spraying synthetic fungicides throughout the growing season. The emergence of resistant powdery mildew populations, to some commonly used synthetic fungicides, highlights the need for research into alternative control methods. Between 2012 and 2015, the efficacy of two different biofungicides (Bacillus subtilis and Bacillus pumilus) and electrolysed oxidised (EO) water were evaluated to determine if they could be a viable replacement for four commonly used synthetic fungicides (fluopyram/trifloxystrobin, triflumizole, quinoxyfen and myclobutanil) in a greenhouse, nursery and commercial orchard. Electrolysed oxidised water and fluopyram/trifloxystrobin significantly lowered disease severity and incidence in all of the locations tested, however, biweekly applications of EO water had little effect on the fungus and weekly applications were phytotoxic in the nursery and greenhouse. Before EO water is implemented into integrated pest management programmes, the optimal spray frequency needs to be evaluated to eliminate its phytotoxic effects. The biofungicides evaluated in this study had minimal effects on powdery mildew severity and incidence and should not be recommended for control on sweet cherry trees. Currently, synthetic fungicides are the best method for the control of powdery mildew as fluopyram/trifloxystrobin was the only fungicide that was successful in lowering disease incidence and severity over the duration of the powdery mildew epidemic in both the nursery and greenhouse. Future research should evaluate integrated pest management strategies, including additional biofungicides, that could supplement and reduce synthetic fungicide applications.