This section is from the book "Commercial Gardening Vol3", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
This disease is the scourge of American viticulturists, and has proved no less in Europe .since its introduction along with American Vines, imported to replace those destroyed by the Phylloxera. The fungus forms various kinds of fruit, one of which was for a long time known as Phoma uvicola, a name which yet crops up in many works on gardening. The point is to remember that this name refers to the disease now said to be due to Guigtiardia. The general features of the disease are well marked, and cannot be mistaken. The leaves usually first show the disease under the form of irregularly circular spots, which often run into each other. These spots are sharply marked, and soon become brown and dead, and are then covered with minute black points, the Phoma fruit of the fungus. On the tips of the young shoots the spots are usually elongated, pale, and become more or less sunk below the general surface of the shoot. The berries usually suffer severely, the entire bunch becoming shrivelled and mummified, and covered with minute black warts representing the Guignardia fruit of the fungus. These shrivelled berries do not fall, but hang on the vine for a considerable time, unless removed, as they should be, along with diseased shoots.
Dr. C. L. Shear, an American plant pathologist, has paid especial attention to this disease, and has found that by spraying with half-strength Bordeaux mixture, commencing when the shoots are 8 in. to 1 ft. in length, the disease can be held in check. Five or six sprayings, at intervals, are generally necessary. If the disease is not checked before the fruit is approaching maturity, then neutral copper acetate, 1 lb. to 50 gall, of water, should be used, as it does not stain the fruit, whereas Bordeaux mixture does at this stage.