The cause of the trouble is not known. Grapes may "rattle" on high land or low land, on poor soil or rich soil, on heavy or light soil. A vineyard may be affected one year and not the next. Grape-growers usually attribute the trouble to faulty nutrition, but applications of fertilizers have not proved a preventive. Old and well-established vineyards seem freer from the trouble than new and poorly established plantings. The most reasonable theory as to the cause of shelling is that it comes from faulty nutrition of the vine, but the conditions so affecting the nutrition are not yet satisfactorily determined.
Ripe-rot or bitter-rot (_Glomerella rufomaculans_) is a disease due to the same fungus causing the bitter-rot of the apple. As the name indicates, the disease usually appears on the fruit at ripening time and under favorable conditions continues after the grapes are picked. It may also attack the leaves and stems. The first indication of the fungus is the appearance of reddish-brown spots which spread and eventually cover the whole fruit. The berries do not shrivel, but the rotted surface becomes dotted with pustules in which the spores are borne. It is hard to tell how much damage this disease does, but it is not usually great and the late applications of bordeaux mixture for black-rot or powdery-mildew are very effective in controlling it.
Crown-gall, now known to be a bacterial disease which causes knots or galls on the roots of various wild and cultivated plants, sometimes attacks grape roots or even the vines above ground. Occasionally, the disease is rather serious, but it is not often to be reckoned with in the vineyard regions of America. Fungicides are useless in combating the disease and all that can be done is to exercise great care in planting infected stock. It is doubtful whether crown-gall ever seriously injures vines in northern regions, although it may occasionally do so in the South.
In California there is a somewhat mysterious disease known as "Anaheim disease," because of its having first made its appearance in the vicinity of Anaheim. As near as can be learned, the disease first appeared in 1884 and then spread rapidly from forty to fifty miles from the point where it began its ravages, causing direct and indirect loss of many millions of dollars, and leading to the abandonment of grape-growing in some parts of southern California. Fortunately, in recent years the Anaheim disease is less aggressive but still does more or less damage. The nature and the treatment of this disease are not as yet fully determined, although several experimenters are studying the trouble. Californians whose vineyards suffer from this disease should apply to the experiment station at Berkeley for the latest information in regard to it.