MILDEW (AS. meledeaw, honeydew. from *mete, Goth. mail', Lat. me!. Gk. dXa, meli, honey + Way, dew). A somewhat indefinite term used to designate a number of plant diseases that are caused lay fungous parasites, as well as spots Paused by microscopic fungi on cloth. paper. leather, glassware, etc. III England the term as applied to plant diseases has a much wider sig nifieance than in the United States. It is there !mule to include what are known in America as cereal rusts and smuts, as well as many other diseases not recognized as due to the mildews proper. In the United States the mildews are divided into two (lasses, the true or powdery mildews, due to fungi belonging to the order Erysiphaecw, and the false or downy mildews eausecl by fungi of the order PeromIsporneele. The powdery mildews attack the leaves. stems, flowers, and fruits of many of our most valued plants. For the most part they fora superficial floor-like patehes of white upon their host plants. The fungus most commonly develops over the surface of the leaves and mends minute suckers through the epidermis, by which they absorb nourishment from the host. They cause distorted and stunted growth. and often the death of the part of the plant affected. During the summer the fungus sends up numerous branehes, which hear myriads of one-celled spores called conidia, by which the mildew is rapidly spread to other plants. Later in the season thick-walled resting spores are produced, by which the fungus is car ried through the winter. These spores have ap pendages of various kinds, by which they retain their attachment to the leaves, and in the spring they develop a new generation of thin-walled spores for the spread of the disease. There are :fluent 1.50 described species of powdery mil dews. and there are few of our plants that are not subject to attack from some of them. Among the common ones injurious to economic plants are the apple, pear, acid cherry mildew• (Pod osphwra oxycantlay), rose mildew (Sphrerothee0 ifonnosa), hop mildew ( Sphwrotheca castaynci), grape mildew (Uncinula spinals), mildew of wheat and other grasses (Erysiphc graminis), gooseberry mildew (i'pha•rothera mors-anr), cu cumber mildew (Erysiphe ciehoraccarum), which also attacks verbenas, sunflowers, asters, and other plants. pea mildew (Erysiphe martii), etc.
Downy mildews are internal parasites w•lhich grow through the tissues of the plants that bear them, and only appearing outside to shed their micro scopic spores. The branches of the fungus hearing the.•e spores are often so abundant as to give a perulhu• downy or frosty appearanee to the leaf or other part of the plant infested. The spores (middle) are one-celled, thin-walled, and are readily blown about by the wind. Falling upon a new leaf or plant, if the moisture conditions are favorable, they quickly germinate and set up a new infection. In this way they spread with great rapidity, and often produce epidemic outbreaks of disease. The resting spores are formed within the tissues of the host, and are thus carried over from season to season. They are liberated by the decay of the tissues sur rounding them, and from these a new generation is derived. Among the downy mildews are some of the most serious plant parasites. The more common ones are the potato rot o• mildew (Phy toidalfora infestans), the grape downy mildew I Ph/80101mm ritieola), lima-bean mildew• (l'hy tophthom phascoli), lettuce mildew (Brenda laetunc), onion mildew (Peronospora sehlcideni am), encumber and melon downy mildew• (Pk/s ampan( enhensis), downy mildew of radishes and other ot•ocirerous plants (Cystopus eandidus), pie. Most of these mildews are more fully de seribed under the diseases of their respective host plants. The problem of conffiating them has been a subject of much experimentation in America and in Europe. It has been found that Many of the powdery mildews can lei held in cheek and often serious loss prevented by dusting the plants with sulphur, or. if in a house or frame where it can be done, exposing them for a few mo ments to the fumes of boiling, hut not burning. sulphur. Spraying thoroughly and repeatedly with Bordeaux mixture, ammoniacal copper carbonate solution, o• other standard fungicide (q.v.) will prevent the serious attack of both classes of mildews. Success in these preventive treatments depends upon thoroughness. See DISEASES OF PLANTS FUNGI, ECONOMIC.