ASCOCHYTA CLEMATIDINA, THE CAUSE OF STEM-ROT 

 AND LEAF-SPOT OF CLEMATIS 



By W. O. Gloyer, 

 Associate Botanist, New York Agricultural Experiment Station, Geneva, N. Y. 



INTRODUCTION 



The sudden dying of clematis plants has been known for many years, 

 and there has been much speculation as to its cause and prevention. 

 Apparently the disease occurs in both Europe and America wherever 

 the large- flowered kinds of clematis are grown extensively. From 

 published accounts it is clear that the various writers had in mind the 

 same disease, though they ascribed it to different causes. In 1884 

 Arthur (i) ^ studied a clematis stem-rot which he suspected of being 

 due to the fungus Phoma clematidis Sacc. Trelease (16), Comstock (3), 

 Klebahn (7), and others have considered nematodes as the causal agent. 

 In specimens received from Klebahn, Ritzema Bos (2) found nonpara- 

 sitic nematodes, while in material of his own collection he found the 

 larvae of a fly, Phytomyza affinis, and a species of Pleospora. Prillieux 

 and Delacroix (9) and Morel (8) believed the disease to be of bacterial 

 origin. Sorauer (13) reports a gall-like formation on the stem of Clematis 

 jackmanni near the surface of the soil and attributes the death of the 

 affected plants to Gloeosporium clematidis. Green (5, p. 284-285) has 

 reported the relative susceptibility of a few varieties of clematis which 

 he grew, but he did not attempt to ascertain the cause of the disease. 

 Except for a preliminary abstract by the writer (4), the primary cause 

 of the clematis disease has heretofore been unknown. 



DESCRIPTION OF THE DISEASE 



The clematis disease manifests itself differently on the various species 

 and hybrids. On hybrids grown in the field it is a stem-rot, while in the 

 greenhouse, where the cuttings are propagated, it is a leaf-spot as well 

 as a stem-rot. On Clematis panicidata the disease takes both forms. 



C. paniculata, a type species, is propagated from seed ^ and when 

 grown in uninfected cold frames or greenhouses remains free from disease. 

 Such seedlings are either potted or placed in beds, where they are planted 

 about an inch apart in rows 4 inches apart. In the fall, when these plants 



' Reference is made by number to " Literatiire cited," p. 341-342. 



^ For description of general methods of propagation and of the various species of clematis see the following: 



Bailey, L. H., ed. Cyclopedia of American Horticulture, ed. 7, v. i, p. 327-333, fig. 485-492. 1910. 



Le Bcle, Jules. The clematises. In Garden, v. S3. no. 1388, p. 544-548, illus.; v. 54, no. 1391, p. 39-40, 

 no. 1395, p. 127; no. 1396, p. 138; no. 1399, p. 200-201; no. 1401, p. 240-241. 1898. Translated from Bui. 

 Soc. Hort. Sarthe, 1896. 



Journal of Agricultural Research, Vol. IV, No. 4 



Dept. of Agriculture, Washington, D. C. July 15, 1915 



N. Y. (Geneva) —a 

 (331) 



