Erysiphe penicillata
Erysiphe penicillata is a plant pathogen that causes powdery mildew on alder.
Image:Oidium (Microsphaera) [spores 160X.png|thumb|Spores of the anamorph of Erysiphe penicillata]
It has also been reported to have affected certain species of Corylus including Corylus sieboldiana, Corylus colurna and Corylus heterophylla, although this is doubtful following Bradshaw et al..