The cluster - cup rust is exceedingly common on wild gooseberries and currants and is known to some extent on cultivated forms. It occurs in Europe, Alaska and in many parts of the United States. Serious damage is seldom reported, although some complaint was made several years ago (1892) of the loss of foliage and fruit on account of an unusual outbreak.
The disease may be recognized in the early summer by the presence of bright, orange - colored cups grouped on reddish, swollen areas on the lower surface of the leaf. Sometimes these structures are found on the fruit, causing distortions.
The cluster-cup rust fungus is Puccinia Pringsheimiana. The orange - colored cups already described contain spores known as seciospores. These are carried to various common sedges, Carex acuta and C. Goodenovii, where infection takes place. Following the development of the mycelium within the sedge leaves, a second type of spore structure, known as a uredineum, is produced; the uredinia bear uredospores. Later a third kind of fruiting body appears; this is known as a telium, and it bears teliospores. In the latter condition the winter is passed. In the spring the teliospores germinate by means of a short promycelium bearing sporidia. The sporidia are blown to the currant and gooseberry, where infection occurs. Finally, the secial cups appear; these bear a fringed margin and are filled with small seciospores.
Usually this rust disease does not cause damage sufficient to warrant particular attention. If it should assume serious proportions, the elimination of rusted sedges in the fall would be essential. No further control measures are known.
Humphrey, J. E. The cluster cup of the gooseberry (Aecidium Grossulariae Schum.). Massachusetts State Agr. Exp. Sta. Rept.
1892:33-34. 1893. Longyear, B. O. Fungous diseases of fruits in Michigan. Gooseberry rust. Michigan Agr. Exp. Sta. Spec. Bul. 25: 48. 1904. Anonymous. Gooseberry cluster - cup disease. London Bd. Agr.
Journ. 14: 428 - 429. 1907. Soppitt, H. T. The gooseberry fungus. Gard. Chron. 3: 24: 145.1898.