Autonomous UV-C application to deal with low and high powdery mildew disease pressure in strawberry

For powdery mildew management, multiple and labour intensive sprayings of biological and chemical fungicides are essential to maintain healthy strawberry crops. However, the decrease in the working rate of active ingredients and the extra-legal demand for less residues on the fruit ask for an alternative solution. An autonomous robot is developed to apply UV-C on tabletop strawberries and a strategy for powdery mildew has been optimized. The goal now is to create a UV-C inclusive IPM strategy for strawberry. Results reveal that night-time application has an increased efficiency compared to daytime application. In this study, we compare the efficacy of UV-C applications at different levels of disease pressure. The spring cultivation in the plastic greenhouse (low mildew pressure) shows a sufficient mildew control with a two times a week UV-C night-time application of 55 or 110 J m^‑2. This UV-C strategy, without any sprayings, competes easily with an intensive, conventional IPM strategy. In autumn cultivation in the plastic greenhouse (high mildew pressure) we had to augment the number of treatments to three times a week at 110 J m^‑2 to have adequate control of powdery mildew. Further elevation of the UV-C intensity to 220 J m^‑2 did not result in the needed effect compared to the more frequent 110 J m^‑2 treatments. Side effects of UV-C are that UV-C harms spider mite (Tetranychus urticae) and beneficial mites (Amblydromalus limonicus). No other main side-effects were revealed. Integration of UV-C in IPM is being realized and if applied correctly, will be a big step forward to sustainable strawberry production.