Oils activity in the control of rose powdery mildew.

The efficacy and eventual phytotoxicity of oils from rape, sunflower seed (vegetable oil) and paraffin (Atpolan 80 EC) in the control of Sphaerotheca pannosa var. rosae were evaluated on roses grown in greenhouse or plastic tunnel. Oils were applied curativelly as plant spray 4-times at 7-day-intervals in concentrations from 0.25 to 4%. All used oils, gave as good effect as triforine (standard) or even better. On shrubs protected with oils at concentrations 0.25% and 0.5%, disease symptoms were noted only sporadically. Rose shrubs sprayed with higher concentration of oils were almost completely protected. Efficacy of tested oils increased with their concentrations. Paraffin oil was better in the control of S. pannosa var. rosae than vegetable oils. After 2 oil applications at conc. 2% or higher, first phytotoxicity symptoms on leaves were noted, particularly during warm and sunny days. Observations of treated leaves, 24 h after spraying under microscope, showed that all tested oils caused hyphae and spores degeneration or their visible deformation suggesting partial loss of turgidity. Depends on oil concentrations used, sporadically regular and unchanged shape hyphae and spores were visible.