powdery mildew Either a fungus of the order Erysiphales or a plant disease caused by such a fungus. The leaves, fruit, etc., of an infected plant bear characteristic powdery white patches of conidium-bearing mycelium; tiny black perithecia may also be visible. Many types of plant may be affected, usually each by its own particular species or strain of fungus.

powdery mildew Either a fungus of the order Erysiphales or a plant disease caused by such a fungus. The leaves, fruit, etc. of an infected plant bear characteristic powdery white patches of conidium-bearing mycelium; tiny black fruit bodies containing haploid spores (perithecia) may also be visible. Many types of plant may be affected, usually each by its own particular species or strain of fungus.