Efficient powdery mildew control with repeated UV-C treatments in tomato

Abstract: In tomato, powdery mildew is caused by Oidium neolycopersici. The severity is
related to the cultivar, and some important cultivars will be infected if the environment
conditions are optimal. Chemical or biological control is used to overcome epidemics. Within
the Interreg NWE program “UV-Robot” we developed a UV-C strategy, applied by a robot, to
control powdery mildew in a tomato cultivation crop. Powdery mildew was inoculated in the
greenhouse. The development was monitored with a scoring system, based on the coverage of
mycelium. The “McKinney disease index” transformed this to a degree of infestation. Several
UV-C strategies, started before inoculation, were tested. This implies a preventive strategy and continued during the whole greenhouse trail. The efficiency of the UV-C strategy was related to three different parameters: (i) An exponential relation between the UV-C dosage and the degree of infestation. (ii) Higher frequency of treatments results in better control. (iii) Night time treatments are then times more effective compared with the same treatments during the day. An intensity of 30 J/m², at night, three times a week, is found as most ideal UV-C strategy in tomato. The night time treatments allow to reduce the dosage and it make it possible to have an intensive treatment schedule without interrupting the daily work at the greenhouse. This preventive strategy reduced the degree of infestation to 13 % in an environment with an artificial high pressure of powdery mildew of 51 % on the controls, without a negative effect on plant health or production.