WHITE-PINE BLISTER RUST. 5 



natural occurrence of the disease shows that dormant Ribes stock 

 docs not harbor the fungus. But all the evidence is negative (except 

 that mentioned earlier by the writer) 1 and is subject to certain 

 limitations, as is all negative evidence, when general conclusions are 

 drawn from it. That is, it does not effectually dispose of possible 

 rare exceptions, which may occur only once in thousands of cases. 

 The practical conclusion is that Ribes plants do not carry the fungus 

 over winter and that an outbreak of this disease on Ribes is to be 

 attributed to the presence of neighboring white pines which have 

 the blister rust. Hence, w T hen the disease is found on Ribes leaves a 

 special effort should be made to locate and destroy infected trees. 2 

 Ewert 3 has recently published a paper showing that thorough spray- 

 ing with Bordeaux mixture, with special care to cover the lower 

 surface of the leaves, will almost completely control this fungus upon 

 Ribes nigrum. It is suggested that in the future when diseased pine 

 trees are found early in the summer, any Ribes in the vicinity be 

 promptly sprayed on both sides of the leaves, in order to reduce the 

 resulting infections and the outbreak of the uredo stage. Spraying 

 should not be resorted to except as a temporary expedient, as just 

 indicated. 



About May 15, 1913, several plants of Ribes nigrum were isolated 

 and an attempt was made to inoculate them with telial material 

 furnished by Stewart which had been kept out of doors all winter. 

 This attempt was unsuccessful, as was also a similar one made by 

 the writer in 1912 with fresh teliospores. 



CULTIVATED VERSUS WILD RIBES. 



A statement has been made implying that the cultivated species 

 of Ribes are not dangerous factors in connection with this disease. 4 

 All of our experience in this country shows that the contrary is true. 

 In no known case has the disease been discovered on native wild 

 species of Ribes, while it has been found in a number of cases on the 

 cultivated species of Ribes nigrum and Ribes vulgare. The evidence 

 shows that our native wild Ribes cynosbati and Ribes prostratum are 

 resistant to the fungus, while Ribes nigrum is exceedingly susceptible, 

 and some varieties of Ribes vulgare are quite susceptible. The variety 

 Red Cross has been found in one instance to be seriously diseased. 

 Ribes grossularia has been immune. The cultivated Ribes are much 



1 Spaulding, Perley. Notes upon Cronartium ribicola. In Science, n. s., v. 35, no. 891, p. 146-147. 1912, 

 The present status of the white-pine blister rust. In U. S. Dept. Agr., Bur. Plant Indus. Circ. 



129, p. 17. 1913. 



2 Spaulding, Perley. Notes on the white-pine blister rust. (Abstract.) In Phytopathology, v. 4, no. 1, 

 p. 41^2. 1914. 



3 Ewert, R. Erfolgreiche Bekampfung des Cronartium-Rostes auf der schwarzen Johannisbeere. In* 

 Ztschr. Pflanzenkrank., Bd. 23, Heft 8, p. 463-47-6, 2 fig. 1913. 



< Clinton, G. P. Notes on plant diseases of Connecticut. In Conn. Agr. Exp. Sta. Rpt., 1909-10, p. 732 

 1911. 



