See:
Greenhouse Plants, Ornamental - Powdery Mildew
Cause The fungus Podosphaera alpina f. alpina has been reported from Washington and British Columbia and found several times by the OSU Plant Clinic. It has not been reported to be a serious pathogen.
Symptoms White colonies on the undersides of leaves.
Cultural control
- Space plant for good air circulation.
- Grow in partial shade.
Chemical control Not many fungicides have this host on the label but others may legally be used. Test first on a small section before applying on the whole plant to evaluate possible phytotoxicity.
- Spectro 90 WDG at 1.53 lb/A. Group 1 + M5 fungicide. 12-hr reentry.
Reference Putnicki, L.S., and Glawe, D.A. 2009. First Report of Podosphaera alpina f. alpina on Tolmiea menziesii in Washington state and British Columbia. Plant Health Progress doi:10.1094/PHP-2009-0810-01-BR.