Figure shows the results of different UV-C treatments in tomato to control Powdery mildew. UV-C treatments were given at day and night time, three times a week. Only in the last object we treated the tomato plants 5 times a week. All the UV-C treatments can reduce the infection of Powdery mildew. The comparison between 120 J/m² at night and day time showed the additive value of night time treatments. Night time treatments are 10 times more efficient than the same dosage applicated during day time. With night time treatments we can conclude that 30 J/m² or max. 60 J/m², 3 times a week, can control the Powerdy mildew without negative effects on the plants.