Powdery mildew. Coloured scanning electron micrograph (SEM) of the parasitic powdery mildew Erysiphe sp. on a leaf. It is an agricultural pest that parasitizes leaves of certain grass, cereal and vegetable plants. The mycelium absorbs nutrients from the plant's epithelial (surface) tissues, and produces erect conidiophores (the club-like structures here), which bear the fungal spores. The conidiophores cover the surface of the plant host, giving it the soft, powdery appearance responsible for the parasite's name.