Podosphaera euphorbiae is a powdery mildew affecting Spurge plants (Euphorbia). The conidia have fibrosin bodies. Despite the name, this is not listed in Woods et al (2024) as affecting Poinsettia

Several other powdery mildews affect some Euphorbia species - see Woods et al 2024 for host plant lists

host

Photograph the mildew on host plant, and add host species to the comments for your record.  If your record is on Poinsettia or Cypress Spurge, microscopic examination or verification by an expert before submission to NatureSpot will be needed.

Euphorbia species