UV-C irradiation after sunset increases control of powdery mildew in strawberries with side-effect on mite populations

For powdery mildew management, chemical fungicides are indispensable to maintain healthy strawberry crops. However, rising chemical resistance and multiple active ingredients left on strawberries ask for an alternative solution. In this study, we test a physical approach to control mildew with UV-C irradiation. A prototype robot equipped with eight 160-W lamps was designed to radiate tabletop cultivations. The robot drives at four speeds that result in four different application doses: 30, 60, 120, 200 J m^‑2. In a glasshouse UV-C was applied three times a week at noon or after sunset throughout the cultivation cycle. Results reveal that mildew is greatly suppressed when UV-C is used at night. With the lowest dose resulting in only 5% disease infection performing better than the highest dose applied at noon. While mildew control is the main goal of UV-C irradiation, side effects on pests and beneficials also need to be assessed. We revealed that they are both positive and negative as spider mites (Tetranychus urticae) and beneficial mites (Amblydromalus limonicus) are harmed by UV-C with a more substantial suppression at night. Our study supports the use of UV-C light to control powdery mildew in strawberries, further research needs to optimize the application strategy to reach compatibility with current IPM practices.