GRAPE DISEASES. Few plants are subject to as many and as serious diseases as the grape, and few plant diseases have been more fully investigated. Diseases of the grape are caused by improper conditions of soil and moisture, but more frequently by fungi and bacteria, which are often carried from diseased to healthy plants by insects. A few of the more destructive and widely spread diseases may be briefly considered here. Downy mildew (Plasntopara viticola or Peronospora viticola) produces yellowish spots upon the upper surface of the leaves and a downy frosty appearance beneath. Later these spots appear as light-brown discolorations. The same fungus occurs upon the fruit, when it is known as 'brown rot' or 'gray rot,' according to the nature of the attack. The brown rot of the fruit is first manifested by purplish discolorations, soon after the appearance of which the pulp be comes soft, and forms depressions, over which the skin is tightly drawn. The gray rot which at tacks the young berries and their pedicels re sembles the downy growth mentioned as occur ring on the leaves. Downy mildew and black rot, next to be discussed, are the two most serious general grape diseases. Black rot (Lce stadia Bidwellii) attacks the leaves at first as reddish-brown circular spots; later a number of spots may coalesce and form irregular blotches. Upon the fruit, the first sign of attack is the appearance of small brownish discolorations, which soon enlarge, the whole berry gradually becomes brown or black, withers, and finally dries up, usually remaining attached to the stem. An thracnose ( Spha celom a ampelinum) attacks leaves, stems, and berries. Upon the leaves it ap pears as dark spots surrounded by well-marked darker bands of color. The centres later turn gray, and frequently the diseased areas fall out, giving the leaves a ragged appearance. Upon the
shoots the disease manifests itself in much the same manner. On the fruit the disease is often termed 'bird's-eye rot,' from the peculiar appear ance of the spots. The centres become gray, with an outer band quite dark and sometimes a zone of vermilion color between them. When the young fruits are attacked they turn brown, and pink pustules appear over the surface. The tissues of the berry with this rot become hard and leathery. Bitter rot (Gkeosporium fructagenum) attacks the stems and fruits, especially the latter, which become bitter, whence the name. In this disease the berries turn brown, become thickly dotted with purplish-black pimples, and ultimately fall at the least disturbance. The best preventive measures for these diseases is thorough spraying with Bordeaux mixture. Powdery mildew (Uncinula spiralis) is trouble some in grape-houses and in the vineyards of France, but less in the vineyards of the United States. It covers the leaves, young shoots, and fruits with a powdery, meal-like growth. Upon the leaves and fruits it forms patches of various size and shape on the upper surfaces. Soon the berries shrivel, the skin cracks, and other agents of decay complete the destruction. For the pre vention of the disease, sulphur is perhaps the best remedy. It may be dusted over the vines in the open, or it may be evaporated without ignition in the grape-house. See FUNGI, EcoNomm; Drs EASES OF PLANTS; FUNGICIDE. Consult: Tubeuf, Diseases of Plants Induced by Cryptogamic Parasites, translated by W. G. Smith (New York, 1897) ; Pierce, "Grape Diseases on the Pacific Coast," in Farmers' Bulletin 30, United States Department of Agriculture (Washington, 1901) ; and the authorities referred to under FUNGICIDE.