Powdery mildew. Coloured scanning electron micrograph (SEM) of the parasitic powdery mildew Erysiphe sp. on the stalk of a plant. The orange needle-like structures are thorns on the surface of the stalk. Hyphae (grey) are the tangled filaments that form the fungal colony. Rising up from the hyphae are asexual spore-bearing structures called conidiophores. Powdery mildew is so-called because of the numerous white spores it produces. It is an agricultural pest, which parasitizes leaves of grasses, cereal and vegetable plants. Magnification: x170 at 6x7cm size.