This is a disease which assumed greatest importance when the practice of piling and sweating apples was in vogue. At present this method of handling the fruit is not in use, consequently Pink Rot gives markedly less trouble. In seasons of unusual dampness outbreaks have resulted in heavy losses. The years 1882, 1894 and 1902 stand out in the history of the apple industry in western New York because of the epiphytotics of Pink Rot. Authorities estimate that thousands of barrels of apples were destroyed in one year in New York State on account of Pink Rot. Experiences have been similar in Ohio, Michigan and Nebraska. Such varieties as the Rhode Island, Fameuse, Fall Pippin, Pound Sweet, Maiden Blush and Twenty Ounce were damaged seriously by Pink Rot under the older methods of orchard practice. The recurrence of such losses, however, should hardly be expected under the present conditions and methods of management. However, the disease still ranks prominently among the minor apple troubles, the fruit being affected on the tree and in storage. The pathogene is fairly common in cellar and commercial cold storage, especially on scabby fruit.
The term Pink Rot is slightly misleading in that the affected tissue is not pink. The name has arisen from the fact that the conidio-phores and conidia of the pathogene are pink in color and stand exposed on the surface of the lesion. Pink Rot very commonly follows apple scab (Fig. 32). Around the superficial, velvety scab spot the apple - tissue becomes brown, sunken, bitter and rotten. Very early in the progress of the disease, the fruiting stalks of the pathogene become evident, at first white and then pink. These symptoms were observed very commonly in the fall of 1915 on scabby Rhode Islands, in New York both before and after harvest. The decayed areas are circular in outline, and vary in diameter, depending largely upon the size of the scab spot which it surrounds, and upon the weather conditions. The lesion is shallow, the affected tissue firm, corky and dry. Growers sometimes call the disease canker, but this name should be avoided.
Fig. 32. - Pink Rot following apple scab.
Pink Rot is a fungous trouble, the pathogene of which is Ceph-alothecium roseum. The organism was discovered in Austria about 1836 and is now known all over the world. The fungus lives commonly as a saprophyte on dead and decaying vegetable matter. Its spores may be found floating in the air almost anywhere. Consequently when a wounded or scabbed surface of a ripe or nearly mature apple is exposed, these floating conidia come to rest on such places, germinate, and their germtubes enter the apple-flesh. Scab-lesions furnish the most common point of entrance. The upturned skin at the edge and the cracks at the center of such spots seem to be particularly adapted to penetration by the Pink Rot organism. The causal fungus cannot enter through the unbroken skin. Sometimes pears, quinces, grapes and plums are attacked in a manner similar to that of the apple.
The history of the disease shows that it was most troublesome in the days when apples were piled after being picked. Under such conditions the fungus found excellent conditions for growth and worked great destruction. Where apples are still so handled, the practice should be discontinued. Fruits that are free from scab are freer from Pink Rot than scabbed apples. It is almost unnecessary to state, therefore, that thorough and timely spraying or dusting for apple scab should be given strict attention. Cold storage keeps the fungus in check but does not kill it, as shown by the fact that it grows vigorously when removed from such storage to a warm room. However, it is recommended that apples be stored in a dry, well-ventilated room where the temperature is kept at 32° Fahr. Apples picked, barreled and immediately stored show noticeably less Pink Rot than those which suffer some delay between harvest and storage. In picking, the fruit should be graded carefully, and suspicious or affected fruits should be discarded.
Eustace, H. J. A destructive apple rot following scab. New York (Geneva) Agr. Exp. Sta. Bul. 227: 367 - 389. 1902. Craig, John, and Van Hook, J. M. Pink rot an attendant of apple scab.
Cornell Univ.. Agr. Exp. Sta. Bul. 207: 161-171. 1902. Ivanov, K. S. Uber Trichothecium roseum Link, als ursache der bitterfaule von fruchten. Zeitschr. f. Pflanzenkrankheiten, 14:36 - 40. 1904