Erysiphe knautiae is a powdery mildew which affects plants in the Scabious family.

Podosphaera dipsacacearum also affects some species in the Scabius family, including Knautia arvensis and K macedonica, Teasels (Dipsacus) and Giant Scabious (Cephalaria).  It looks very similar but the conidia have fibrosin bodies which are not present in Erysiphe knautiae

host/microscopy

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Affects plants in the Scabious family, including Knautia arvensis (Field Scabious), Knautia macedonica, Scabiosa columbaria (Small Scabious) and Succisa pratensis (Devil's-bit Scabious).