oidium

noun (plural oidia /-dɪə/)

• 1 Botany a type of fungal spore (conidium) formed by the breaking up of fungal hyphae into cells, especially as produced by powdery mildews.

• 2 [mass noun] a fungal disease affecting vines, caused by a powdery mildew.

  • The fungus is Uncinula necator (formerly Oidium tuckeri), family Erysiphaceae, subdivision Ascomycotina