MILDEW (Ger. Mehlthau, meal-dew), a term of somewhat vag-ue application to cer tain diseased states of plants caused or characterized by the growth of small parasitical fungi, and also to spots on cloth, paper, etc., and even on the surface of glass and other inorganic substances, produced by the growth of minute fungi. The mildew fungi are numerous, and the name mildew is often given to many that are also known by other names, as BLIGHT, BRAND, BUNT, RUST, etc.; see these heads; see also BOTRYTIS and ()mum. Different species or families of plants have their own peculiar parasites; several kinds of parasitic fungus being, however, often known to infest one plant. Probably, the name mildew originally belonged to those molds which form white mealy patches on leaves. Some of these belong to the genus Erysiphe, which exhibits fleshy somewhat gelatinous masses, becoming globose sporangia, filled with spore-containing asci, and surrounded by a flocky mycelium, often spreading widely over the leaves and other parts of plants. Maples are sometimes covered with a mildew of this kind, so as to be quite hoary. Similar mildews are often seen on peas and other leguminous plants; also on
umbelliferous plants. Sulphur has been found effectual in curing some of these mil dews. Many of the most destructive mildews are of a red or brown color, as the mildew of the pear, Aecidium cancellatum, that of the barberry, Aecidium Berberidis, etc.; whilst some are almost black, as the corn mildew, Puecinles graminis, by which the crops are in some years greatly injured.
Whether tnildew is the consequence of unfavorable weather and of fungi attacking an already weakened plant, or is the consequence of infection by spores of fungi brought through the air or soil to a plant previously healthy, is not yet well ascertained; and probably the one may be sometimes the case, and sometimes the other. There is no doubt that many kinds of mildew appear chiefly toward the close of summer on leaves in which vegetable life has already in a great measure lost its power.