mildew, name for certain fungi and protists, for the diseases they cause in various crops, and for the discoloration (and sometimes the weakening and disintegration) they cause in such materials as leather, fabrics, and paper. The powdery mildews usually grow on the surface of plant tissues, forming a gray or white coating and absorbing nourishment from the host. Although traditionally considered fungi, the downy mildews are now more often considered protists. They attack grapes, cucumbers, potatoes, and other vegetables. Methods of making fabrics and leather resistant to mildew have been devised. For the occurrence and control of mildews in agriculture, see diseases of plants. Powdery mildews are classified in the kingdom Fungi, phylum (division) Ascomycota; downy mildews are classified in the kingdom Protista, phylum (division) Oomycota.

Conspicuous mass of threadlike hyphae (see mycelium) and fruiting structures produced by various fungi (kingdom Fungi; see fungus). Mildew grows on cloth, fibres, leather goods, and plants, using these substances as food for growth and reproduction. Downy mildew and powdery mildew are plant diseases that affect hundreds of species.

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