This disease is sometimes called anthracnose, but it should not be confused with the anthracnose disease discussed on page 249. The name Bitter Rot is also used to designate this trouble, although Ripe Rot is preferable.
Ripe Rot was known several years prior to 1887, at which date grape diseases first received the serious attention of American plant pathologists. The history of the disease shows that the first observations on it in the United States were made in North Carolina, although the pathogene was described in England in 1854. At present the disease has a general range over the grape regions of the country, but only occasionally is there any wide devastation. White varieties, like the Martha, are sometimes affected in a destructive fashion. A characteristic of the disease which makes it annoying and dangerous is that even after a crop has escaped other grape diseases during the year, ripe or ripening berries may be attacked to a considerable extent.
Berries, canes and fruit-pedicels may be affected by Ripe Rot, but it is most conspicuous on the berries. Ripe grapes only are affected; or at least they are not affected until the ripening period is near at hand. The diseased flesh becomes reddish brown or rosy in color and the surface is sunken. Finally the lesion, by enlarging in concentric zones, involves the whole berry, and the result is a brown or purple mummy. The lesions are more striking on light-skinned varieties. These characters serve to distinguish Ripe Rot from Black Rot. It has been noticed ' that Ripe Rot mummies fall to the ground at the slightest jar, while Black Rot mummies cling tenaciously to their pedicels. Affected berries are not bitter, as the name Bitter Rot would suggest. The name Bitter Rot has been adopted in the several cases on account of the fact that the same disease occurs on apples, on which it is known as Bitter Rot.
Ripe Rot of grapes is caused by the well-known fungus Glomerella cingulata. The fungus occurs on a wide range of plants, including many fruits. Its mycelium permeates the affected tissues, and even enters the seeds of the grape-berry. A cushion of mycelium develops just below the upper wall in a group of epidermal cells. As it increases in size the cushion - the fruiting body - pushes upwards, rupturing the epidermal walls. In this way the fungus exposes its fruit - body to the air; spores are developed and may be liberated with little hindrance. The pathogene may readily pass from the grape to the apple and back again.
The fungus is favored by excessive humidity and hence is most to be feared when such conditions prevail at the ripening period.
The lateness of the attack of the fungus on grapes makes it difficult to control. It is claimed, however, that if the later applications for Black Rot are made thoroughly, the Ripe Rot disease will be largely prevented. (See page 235 for Black Rot control.)
More complete data concerning the fungus as it occurs on apple are given on pages 14 to 21.
Scribner, F. L. Bitter Rot of grapes. U. S. Agr. Comm. Rept. 1887:
324 - 325. 1888. Galloway, B. T. Ripe rot of grapes and apples. U. S. Agr. Comm.
Rept. 1890: 408. 1890. Lodeman, E. G. Some grape troubles of western New York. Ripe rot. Cornell Univ. Agr. Exp. Sta. Bul. 76: 448. 1894. Southworth, E. A. Ripe rot of grapes and apples. Journ. Myc. 6:
164-173. 1891. Quaintance, A. L., and Shear, C. L. Insect and fungous enemies of the grape east of the Rocky Mountains. Ripe Rot. U. S. Agr. Dept.
Farmers' bul. 284:35 - 36. 1907.