INTERRUPTION OF THE NIGHT PERIOD BY UV-B SUPPRESSES POWDERY MILDEW OF ROSE AND CUCUMBER

Experiments were conducted to determine the optimum dose of UV-B (280-315 nm) required for suppression of powdery mildews of rose (Rosa × hybrid) and cucumber (Cucumis sativus). Daily exposure to UV-B during dark at 1.2 W m^-2 for 2 to 5 min substantially suppressed powdery mildew in ‘Toril’ pot roses without measurable damage to the plants. Compared with the non-UV-B treated control, mildew severity nine days after inoculation was reduced by a factor of 2.6 or 51 times after daily exposures of 2 or 5 min, respectively. In ‘Confida’ cucumber, the optimum exposure time to suppress powdery mildew was 5 to 10 min. Brief night time exposure to UV-B may provide a non-chemical option to suppress powdery mildews in greenhouse crops, where such pathogens have been historically problematic, and fungicide resistance problems are a continuing challenge.