Erysiphe prunastri is a powdery mildew found on on Prunus spinosa (Blackthorn) and other Prunus species.

Several other powdery mildews affect Prunus species - refer to Woods et al (2024) for more details.  Microscopic examination is needed to separate them - see Phyllactinia mali, Podosphaera ampla, Podosphaera pannosa, Podosphaera pruni‐avium, Podosphaera pruni‐lusitanicae, Podosphaera tridactyla.  

host/microscopy

Photograph on host plant, and add host species to the comments for your record.  Microscopic examination or verification by an expert before submission to NatureSpot may be needed

Blackthorn (Prunus spinosa) and similar species: Bullace (Prunus domestica ssp interstitia), Cherry Plum (Prunus cerasifera), St Lucie Cherry (Prunus malaheb), Bird Cherry (Prunus padus) - ref. Woods et al, 2024