This disease has been reported only from Colorado and New York. It probably occurs elsewhere. Both black and red varieties of raspberries are affected. In Colorado it is regarded as a very important trouble. It ranks well up with other factors responsible for marked decrease in production such as late frosts, poor management and age of plantations. It reduces the crop by reducing the number of fruit - spurs. Buds are killed and leaves may die. From 2 to 50 per cent of the canes are lost through their brittleness; for when brittle they break easily while being put down in the fall or taken up in the spring. In New York the disease is far less injurious than in Colorado.
The disease is first apparent in July. The lesions, one to several on a cane, are sharply defined, conspicuous, and measure from one to four inches long and may half-Way girdle the cane (Fig. 122). Spots are found on the nodes near the ground. They may also occur on the internodes and petioles of the leaves. An area about the buds at the base of the leaves becomes brown, the buds shrivel and become dry. The buds then are either weakened considerably, so that they make only feeble growth the following spring, or they die. In the former case the buds come out, but are small, soon turn yellow, and die. On account of this disease fruit - spurs may not be found for two feet above the ground. However, berries are produced on the upper half. Lesions on the nodes and internodes may coalesce so that the whole lower portion of a cane may become dark. The affected bark splits longitudinally, thus allowing the cane to dry out prematurely. As a result of this desiccation the cane is more brittle than normal. The lesions become whitish at the center in September and October. Later small black pustules develop.
Fig. 122. - Spur Blight of raspberry.
The fungus Mycosphcerelld Rubina causes Spur Blight. Its mycelium invades the cortex, wood and pith. Within two weeks after the fungus falls on the spur a typical lesion is produced. The fungus apparently hibernates as immature perithecia in the canes. In the spring these bodies mature their ascospores. This occurs about the first of May. These spores are liberated and are carried by the wind to young canes which are at this time but a few inches high.
It has been demonstrated in Colorado that spraying will prevent Spur Blight. The time of inoculation necessitates that spraying be done early in the spring. Bordeaux mixture 3-2-50, with the addition of resin-fish-oil - soap at the rate of two pounds to fifty gallons of bordeaux as a sticker, is advised. Apply to the young canes only, and care should be taken to coat the portion nearer the ground. Four applications are advised; three before picking at intervals of two weeks and one immediately after picking. The first application should be made when the plants are only a few (eight to twelve) inches high. This is the last of May in Colorado. The second spraying follows two weeks later. The third two weeks after the second. Old fruiting canes should be removed and burned immediately after harvest to prevent infection of new canes.
Sackett, W. G. Spur blight of the red raspberry caused by Sphaerella rubina. Colorado Agr. Exp. Sta. Bul. 206: 3 - 26. 1915.
Robbins, W. W., and Reinking, O. A. Fungous diseases of Colorado crop plants. Raspberry. Spur blight. Colorado Agr. Exp. Sta. Bul. 212: 45. 1915.
Stewart, F. C, and Eustace, H. J. Raspberry cane blight and raspberry yellows. Relation of cane blight to the discolored areas on red raspberry canes. New York (Geneva) Agr. Exp. Sta. Bul. 226:354 - 358. 1902.