This disease was first observed in 1899 in the Hudson Valley, State of New York. Until that time it was wholly unknown to science, although it was then abundant and destructive.
Later reports indicate that raspberry Cane Blight now has a very general range in the plantations throughout New York State. Its geographical distribution over the United States is not well known, but it is doubtless common throughout the country. It has been seen in Ohio, Wisconsin, Connecticut and a few other states.
The chief damage is done to the fruiting canes. New canes are attacked, however, and occasionally are killed during the first season of their growth. This is not the most important raspberry disease generally, and rarely is a whole crop lost. On the other hand, few plantations are entirely free from it, in New York at least, and cases are on record where one-fourth to two-thirds of the crop was lost through the effects of Cane Blight. It may easily be imagined that the aggregate losses in the country must be considerable. It is said that Cane Blight is often partly responsible for the early decline in the productivity of both the red and black raspberry plants. Death of the affected canes at the point of attack results in a wilting of both the cane and its foliage. Hence, the disease is sometimes called raspberry cane - wilt. In such cases the berries become dry and worthless. In many instances the berries are attacked directly, resulting in a dry rot.
The disease affects nearly all of the red and black varieties, and perhaps also the dewberry and wild red raspberry (Rubvj strigosus). There is nothing to indicate the occurrence of Cane Blight on the blackberry, except on wild species. Among the commercial raspberries, the Cuthbert variety probably suffers most. Other varieties, such as the Marlboro, Ohio, Gregg, Kansas, Superlative, Pride of Geneva, Parmer and Cumberland, are affected considerably. The Columbian is notably resistant.
Observations indicate that the disease may be expected to appear in neglected and well-managed plantations alike. The lesions are found most commonly on the canes (Fig. 120), although the berries may be directly affected. All or only a portion of a cane is involved, in which case the foliage suddenly wilts and becomes dry. Often only a single branch wilts; the remainder of the plant then continues normal activities and appearances (Fig. 120). Frequently only a portion of a cane is blighted, such symptoms becoming evident as soon as the leaves unfold in the spring. Lesions commonly center about a wound left in pruning, from which point they extend downward. There is a tendency on black varieties for the disease to affect only one side of a cane. The diseased area is brown and the cane becomes very brittle at such points. Very early in the blighting of a cane, black fruit-pustules of the pathogene appear on the lesions (Fig. 121); from these pustules masses of reproductive bodies ooze out on the bark, giving the affected portion a brownish smoke - colored appearance. The spots are not always limited in extent; in some cases they are generalized, the wood cracks, and the bark peels off at the lower portion of the affected cane.
The Cane Blight disease may be confused with the work of the raspberry-cane borer (Oberea bimaculata). But in caneblight no insect burrows are found. The disease has also been confounded with drought and winter injury. Drought-injured canes dry up slowly and more uniformly; blighted canes die suddenly. Winter - injured canes do not put out new leaves on the affected portion; blighted canes develop new leaves on the affected parts.
Fig. 120. - Raspberry Cane Blight; healthy plants on right, blighted canes on left.
The berries dry up as a result of cane - wilt (Fig. 120). They are also susceptible to direct attack. This is evidenced by the fact that a single berry in a cluster, or even one side of a berry, may be diseased. The normal green color is slightly tinted as if ripening prematurely; finally, the tissues gradually turn brown and a dry rot results.
The brown mass of reproductive bodies, already mentioned, which ooze out on the affected bark are the conidia of the causal fungus, Leptosphceria Con-iothyrium. These spores are disseminated from plant to plant probably by insects (tree crickets), wind and dashing rain, by pickers, pruners and cultivating tools. The spores germinate on the canes, and evidently the germtubes are capable of penetrating the unbroken epidermis of the canes. The fungus also enters the canes through wounds; stubs left exposed in heading back and injuries made by the snowy tree cricket (Cecanthus niveus) are common points of entrance. Berry-infection doubtless occurs through the flowers and very young fruit. The mycelium works between and within the fleshy parts, of the drupelets, but not in the embryo or stony part. It passes from the fruit down the pedicels and thence upward to other berries of the cluster. The fungus evidently hibernates as pycnospores in pycnidia; in the spring these spores ooze out on the bark. Dead and decaying canes are sources of the inoculum. It has been shown that the fungus may live as long as four years on fallen dead canes. It is believed that the pathogene is carried in the soil particles on nursery-stock. Furthermore, the practice of laying down and covering of canes with soil in the fall to protect them from winter injury, is thought to spread the organism. A perithecial stage has been discovered, but its role is unknown.
Fig. 121. - Cane Blight; fruit bodies of the patho - gene on raspberry cane.
It is peculiar that the fungus may cause most serious damage in dry seasons. This is explained on the grounds that canes become infected during the first season of their growth, but do not show effects until the following year. Weather conditions have a positive influence on inoculation and incubation, but not on the growth of the fungus in the cane.
No definitely established remedial measures are at hand. Ordinarily plantations may be expected to recover, even if badly diseased for one year. As a precautionary measure, plants should not be selected from nurseries in which the Cane Blight is present to any great extent. Since the fungus may live on fallen canes for four years, it is inadvisable to replant on soil within this time after a severe attack. In any case the old canes should be burned. Dead and diseased canes should be removed soon after the fruiting - season, and again in the early spring. If the disease is particularly troublesome, look for any wild blackberries and wild red raspberries in the vicinity of the plantation. Their destruction is one step toward eliminating the fungus.
According to present knowledge, the application of fungicides is not promising. In some cases bordeaux mixture has been applied as follows: (1) when the canes are a few inches high; (2) subsequently at intervals of two weeks until the middle of September; and (3) again the following spring from the bursting of the buds to the setting of the fruit. Future experience may prove spraying a more beneficial measure of control.
Stewart, F. C, and Eustace, H. J. Raspberry cane blight and raspberry yellows. New York (Geneva) Agr. Exp. Sta. Bul. 226: 331 - 366. 1902.
Stewart, F. C. Notes on New York plant diseases, I. Cane blight, Leptosphceria Coniothyrium (Fckl.) Sacc. New York (Geneva) Agr. Exp. Sta. Bul. 328: 387 - 389. 1910.
Jackson, H. S. Raspberry cane blight. Oregon Crop Pest and Hort. Bienn. Rept. 1911 - 1912: 264. 1913.
Gloyer, W. O., and Fulton, B. B. Tree crickets as carriers of Leptosphceria Coniothyrium (Fckl.) Sacc. and other fungi. New York (Geneva) Agr. Exp. Sta. Technical Bul. 50: 1 - 22. 1916.
Clinton, G. P. Notes on fungous diseases, etc., for 1906. Raspberry wilt, Leptosphceria Coniothyrium (Fckl.) Sacc. Connecticut Agr. Exp. Sta. Rept. 1906: 321 - 324. 1907.