Greenhouse Plants, Ornamental - Powdery Mildew
Cause Powdery mildew has been found several times by the OSU Plant Clinic. Three powdery mildew species, Erysiphe sedi, Erysiphe umbilici and Golovinomyces orontii (formerly Erysiphe orontii) have been reported to infect Sedum spp. in different parts of the world. Erysiphe sedi has been found in North America (New York). Although most sedums have good resistance to powdery mildew, S. 'Matrona' is very susceptible.
Symptoms In Europe the disease produces white powdery mildew colonies and abundant sporulation on both surfaces of leaves, petioles, and stems. The fungus appeared on older leaves and then spread upward, causing severe defoliation.
In New York, circular patches of gray mycelia appeared and spread on upper and occasionally on lower leaf surfaces followed by necrosis of the leaf tissues and defoliation. The disease may appear as white or scabby tan to gray patches or as black diffuse spots.
In the PNW, the disease has resulted in stem dieback and ringspots on leaves.
- Space plant for good air circulation.
- Grow in full sun on well drained soil or media at neutral to slightly alkaline pH.
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.
- Eagle 20 EW at 6 to 12 fl oz/100 gal water is registered for landscape, greenhouse, and nursery. Group 3 fungicide. 24-hr reentry.
Reference Kiss, L., and Daughtrey, M.L. 2001. First report of Erysiphe sedi on Sedum spectabile in North America. Plant Disease 85:1207.
Jankovics, T., and Szentiványi, O. 2006. First report of powdery mildew on Sedum alboroseum in Europe. Plant Pathology 55:297.