Powdery mildew of astilbe

The causal agent of powdery mildew on astilbe is the fungus Podosphaera astilbicola (formerly known as Sphaerotheca astilbicola), which belongs to the section Sphaerotheca. Species from the Erysiphe aquilegiae group may also be involved in the pathogenesis. A characteristic powdery coating forms on the affected plant organs, which over time densifies into a felt-like state.

The disease primarily affects the upper side of the leaf blade, although mycelium can spread to the undersides of leaves, stems, and flower stalks. Infection leads to yellowing of tissues, curling, brittleness, and premature death, which significantly reduces the ornamental value of the crop and stunts its growth.