How to effectively control powdery mildew on cucumber plants

Two weeks ago, the last UV-C treatment was given in the cucumber trials of the project. The last trial served as a demonstration and validation, focusing on the effectiveness of UV in treating powdery mildew. Two varieties were tested, Dee Viate (DV) and Sepalin (SP), both with 50 J/m² UV (UV) and without (CC). Additionally, objects were added for Dee Viate; one where UV was combined with a preventive biological treatment (BUV) and another where a reduced amount of UV was given on darker days (VUV).

The research showed even better results compared to previous trials. During the first six weeks of treatment (phase 1), the powdery mildew infection was more severe in objects without UV, despite the application of chemical treatments once a week. In the next five weeks (phase 2), the chemical treatments managed to slightly control the mildew pressure a better than the UV-treatments. However during these five weeks, again four applications of chemical products had to be executed, whereas during the whole cultivation no treatments –  biological or chemical – were used in the object with UV. Combining UV with a preventive biological fungicide (BUV) improved the effectiveness even a bit more. Utilizing lower doses on days with lower solar radiation resulted in a higher infection rate. The object with lower doses (VUV) shows a nice effectiveness, but the continuous dose of 50 J/m² still controls powdery mildew better.

Against expectations, the production was better in the objects with UV in this trial. Especially, for Dee Viate, the difference was quite clear (22% more). In previous experiments, UV had a slight negative effect on the plants, causing phytotoxicity and resulting in a lower production. This effect seemed to be more severe during darker periods. However, in this trial, the planting date was end January; the cultivation did not receive a lot of solar light and it might be possible that UV light was received as an extra light boost by the plants. It would also explain why Dee Viate, a summer variety that needs more light, shows a stronger advantage with UV than Sepalin.

This validation trial demonstrates that we can effectively control powdery mildew on cucumber plants through a combination of 1) a three-night treatment with UVC light at a dosage of 50J/m², 2) limited application of biological chemicals, 3) using a resistant variety and 4) applying chemical correction when facing higher powdery mildew pressure.