This is a disease which appears to some extent every year, and only occasionally does it become epiphytotic. In New York it was serious in 1889 and 1901, and is one of the most common fungous diseases of the currant in Oregon. The trouble is known throughout the United States and Europe. It is also reported from Asia and Australia. Its origin is unknown, but the first mention of it in America comes from Connecticut, having been found there on black currants in 1873. Subsequently it was discovered in the Adirondack Mountains on the fetid currant, in Iowa on the red currant, and is now known to affect several other kinds of currants - both red and white. Gooseberries are also subject to the disease.
The injury from anthracnose, also known as Leaf Spot and Leaf Blight, comes from its effect upon the leaves and fruit. Plants are known to have been completely defoliated by July 10, and a loss of one-half to two-thirds of the crop of fruit is on record. This early defoliation interferes with the proper ripening of the wood and the formation of fruit-buds for the next year. The disease also affects unfavorably the quality of currants for wine. Old plantations are said to suffer more than young ones, yet the disease is of considerable importance in the nursery. In the nursery older bushes usually suffer more than the first-year cuttings, due perhaps to the fact that the young cuttings are planted on ground which is not ordinarily used for currants and gooseberries. Cuttings in close proximity, however, to the older diseased bushes are very likely to become affected. Although both red and white currants are susceptible to anthracnose, some differences in resistance are noticeable. It has been observed that the Albert variety is resistant and the Fay and Victoria, growing in close proximity to the Albert, may be seriously affected. Again, the White Grape and Wilder are susceptible, while the Moore Ruby and Perfection varieties are resistant. Symptoms. The disease is primarily a leaf-trouble (Fig. 54), although it also shows on the petioles, young canes, fruit - stalks and fruits.
Fig. 54. - Currant anthracnose lesions on leaves.
The attack is made first on the older leaves, and as a result they become thickly dotted with small dark brown, circular spots, chiefly on the upper surface (Fig. 54). When the trouble assumes large proportions, the leaves turn yellow and fall prematurely. On the berries the spots are small, resembling Fly Specks. On the fruit-stalks, the lesions are larger and. may be one-fourth to one-half an inch in length and may extend halfway around the stem. On the leaf-petioles, conspicuous, black, slightly sunken spots are formed. The anthracnose is sometimes confused with Leaf Spot (see page 203), but can readily be distinguished from it by the smaller size of the spots.
This is a fungous disease, the cause of which is Pseudopeziza Ribis. The fungus is carried through the winter by either the conidial or the sexual stages and possibly as mycelium in the canes. The infected leaves fall to the ground in the autumn, and the fungus then penetrates all the tissues. Later it develops an apothecium. In the spring ascopores ripen and are carried to the new leaves, probably by the wind, although no observations have been made on this point. The time of inoculation is unknown, but severely infected plants have been seen on June 8. It is known that about two weeks are required for germination, penetration and the production of visible signs of the disease, from which it may be reasoned that inoculation occurs about the middle of May. The germtube within the leaf, or other susceptible part of the plant, develops mycelium which grows in localized areas and kills the tissues, resulting in the formation of the lesions already described. The mycelium finally forms a mat near the center of the spot where an acervulus develops. At maturity this structure ruptures the epidermis, liberating the conidia in gelatinous masses. These spores are disseminated by rain and insects, but, on account of their gelatinous character, probably are never carried by wind. The conidia continue to propagate the pathogene throughout the growing - season, thus accounting for the extent of the disease in a local area. Conidia produced in late summer are capable of living through the winter. Although, as previously stated, mycelium in the canes may possibly tide the fungus over winter, yet there is considerable evidence to the contrary.
It has been conclusively shown that bordeaux mixture 5-5-50, or lime sulfur solution 1-40 or 1-50, when applied at the right time, is effective in the control of anthracnose. It has recently been found that dusting with the sulfur-lead mixture (90 parts finely ground sulfur to 10 parts powdered lead arsenate) is equally effective. It is essential to make the first application of the fungicide before the discharge of any asco - spores; as previously noted, this occurs during the middle of May. It is further essential to keep the foliage protected throughout the summer. Make the first application when the leaves are unfolding; apply the fungicide at intervals of ten to twenty days until five or six sprayings have been made. The interval may be lengthened and the number of applications reduced in dry weather. In a wet season more frequent applications are necessary.
Since the fungus hibernates in the fallen leaves, it seems logical that these should be destroyed by plowing or some other means. However, there would in all cases be enough leaves to act as an abundant source of trouble.
Stewart, F. C, and Eustace, H. J. An epidemic of currant anthracnose.
New York (Geneva) Agr. Exp. Sta. Bul. 199: 64-80. 1901. Jackson, H. S. Currant diseases. Anthracnose. Oregon Crop Pest and Hort. Bienn. Rept. 1911-1912: 266 - 267. 1913. Dudley, W. R. Anthracnose of currants. Cornell Univ. Agr. Exp.
Sta. Bul. 15: 196 - 198. 1889. Stewart, V. B. Some important leaf diseases of nursery stock. Anthracnose of currants and gooseberries. Cornell Univ. Agr. Exp.
Sta. Bul. 358: 194 - 198. 1915. Clinton, G. P. Currant anthracnose. Connecticut Agr. Exp. Sta.
Rept. 1913: 12 - 13. 1914. Stewart, V. B. Dusting nursery stock for the control of leaf diseases.
Experiment for the control of the leaf spots of currants. Cornell Univ. Agr. Exp. Sta. Circ. 32: 8 - 9. 1916.