Currant Cane Blight or necrosis, also known as wilt and blight, affects chiefly the cultivated varieties of the red currant (Ribes vulgare). It is also found on the cultivated varieties of the black currant (Ribes nigrum), and the European gooseberry (Ribes Grossularia). The Wilder currant is said to be very resistant to Cane Blight.
The disease has been more or less under the careful observation of American pathologists during the past quarter of a century. In 1899 it was studied in New York State under the name of Cane Blight. More recently (1911) it has again been given detailed attention in New York. It occurs in Delaware and probably elsewhere, although its confusion with another trouble has made the determination of its range difficult. The history of Cane Blight shows that it may become epiphytotic in regions where it is established.
The conspicuous symptoms of Cane Blight consist of a sudden wilting and dying of parts or of whole bushes here and there throughout a plantation. This occurs during the summer, at any time while the plants are in leaf. The leaves wilt, turn brown, and die on certain canes or portions of canes. Finally the leaves fall. The affected wood of a cane is killed at a point some distance below the wilted foliage.
Currant Cane Blight is due to the work of a fungus, Botryo-sphceria Ribis. It attacks the canes, and the symptoms just described result. It was formerly thought that the disease was due to Nectria cinnabarina. The fungus B. Ribis passes the winter in the young blighted or dead shoots, or in small cankers. With the advent of the growing-season the pathogene invades and blights the parts below. The spores of the fungus, which develop on the affected parts, may be carried to other plants by the wind or the American currant-borer. It is suggested that the beetle's habit of oviposition may have some relation to the dissemination of the fungus. The currant is most easily infected, that is, most susceptible, during its period of transition from active elongation-growth to that of the maturation - stages. Within a week or two after the spores of the fungus are deposited upon the currant, signs of disease appear. The bark, wood and pith are invaded by the mycelium. Sometimes the leaves also are attacked. The mycelium may be observed in the pith as a fine, whitish, webby growth.
Shortly after early infection occurs, the fungus forms a simple spore-stage on the withering tips. This is known to pathologists as the Macrophoma-form. Following the development of this stage, from midsummer to autumn, a stromatic form appears; this is called the Dothiorella-stage. This form shows as small, globose, sclerotic bodies on the shoots which have been killed in the earlier part of the season. Toward the end of the summer the stromata of the second or Dothiorella - type, instead of forming pycnidia, develop perithecia. In this condition the fungus passes the winter. The following May and June pycnospores are formed. They are discharged the latter part of June or in early July. At the same time ascospores develop within the perithecia already mentioned. Thus pycnidia and perithecia may be found on old dead canes together.
At the present time there is no method of treatment for currant Cane Blight which can be confidently recommended. It has been shown that summer pruning, that is, the systematic removal of all diseased canes at frequent intervals during the spring and summer, is of no value so far as the control of Cane Blight is concerned. Winter pruning is also inefficient, owing to the difficulty of recognizing affected canes while the plants are devoid of foliage. The careless piling of pruned canes along fences should be avoided. Such brush should be burned before the end of May, in order to destroy the fungus.
Stewart, F. C. An experiment on the control of currant cane necrosis by summer pruning. New York (Geneva) Agr. Exp. Sta. Bul. 357: 1 - 10. 1913.
Grossenbacher, J. G., and Duggar, B. M. A contribution to the life-history, parasitism, and biology of Botryosphaeria ribis. New York (Geneva) Agr. Exp. Sta. Tech. bul. 18: 114 - 190. 1911.
Durand, E. J. A disease of currant canes. Cornell Univ. Agr. Exp. Sta. Bul. 125: 23 - 38. 1897.
Chester, F. D. A blight of currants. Delaware Agr. Exp. Sta. Rept. 14:43 - 44. 1903.