The most used and effective strategy to control fungal diseases in fruit growing is the application of fungicides. The use of fungicides , however, can have a negative impact on the environment and its frequent use enhances the risk of fungicide resistance. Moreover, stronger limits concerning the maximum residue levels (MRLs) on fruits are set up by retailers and the export industry. In the future it will be a great challenge to produce fruits of high quality with a minimal input of pesticides. As such, a search for alternative methods, like biological control agents or physical treatments, which are able to efficiently reduce fruit diseases is required.

To this end a physical technique, ultraviolet light in particular, was developed by Clean Light Inc of The Netherlands.

This technology was tested by PC Fruit for its capacity to reduce powdery mildew infestation on apple and strawberry leaves. The applied exposure doses ranged from 5 to 60mJ/cm2. The effect of UV-c radiation was tested on the establishment of powdery mildew on leaves of apple seedlings and strawberry plants. For both apple and strawberry the powdery mildew infestation was significantly reduced by exposing the leaves of both plant species to UV-c with a dose of 30mJ/cmÇ, without negative effects on plant performance . The obtained efficacy levels were comparable with specific fungicide treatments. A regular application in the time was better than using higher dose rates with longer intervals between applications. Results of these trials under controlled conditions will be presented.