PLUM BLOTCH, A DISEASE OF THE JAPANESE PLUM, 

 CAUSED BY PHYLLOSTICTA CONGESTA HEALD AND 

 WOLF^ 



By John W. Roberts, Pathologist, Fruit Disease Investigations, Bureau of Plant 

 Industry, United States Departinent of Agriculture 



INTRODUCTION 



In June, 1905, W. M. Scott of the Bureau of Plant Industry, United 

 States Department of Agriculture, collected near Fort Valley, Ga., fruits 

 of the Japanese plum (Prunus triflora Roxbg.) affected with a disease 

 very closely resembling the apple blotch, due to Phyllosticta solitaria 

 E. and E. In the diseased areas were spore-bearing pycnidia which were 

 found also on the leaves in gray papery spots resembling those on apple 

 leaves caused by Phyllosticta solitaria. On May 27, 1908, the disease was 

 again observed by Scott on both fruit and foliage of the Burbank plum at 

 Montezuma, Ga. It was found to be rather common in several orchards 

 about Montezuma, in some cases causing enough damage to injure 

 seriously the market value of the fruit. In one orchard a large part of the 

 fruit was affected, and many specimens bore from 15 to 20 spots each. 



On May 29, 191 7, the writer collected near the same locality Japanese 

 plum fruits and leaves affected with the same disease. In the single 

 orchard in which the disease was found, most of the fruit was heavily 

 nfected and rendered nearly worthless. Considerable difficulty was 

 encountered in finding the disease again, as the Japanese plum industry 

 in Georgia had about passed out. Lack of demand for the fruit coupled 

 with the susceptibility of all parts of the tree to various diseases and 

 insect pests had caused growers either to eradicate their trees or to let 

 them die. At present there are almost no Japanese plum orchards 

 remaining in Georgia, and all of the trees in which plum blotch was found 

 have been eradicated. So far as the writer knows, then, the disease no 

 longer exists, though it is to be looked for throughout the South as far 

 west as Texas. Should the growing of Japanese varieties of the plum 

 be revived in the South, blotch may prove to be one of its most serious 

 diseases, as it is very destructive, and probably would be exceedingly 

 difficult to control. 



The varieties found to be affected were Abundance, Burbank, and what 

 was apparently an unnamed seedling. 



1 A brief description of this disease was published as an abstract of a paper presented at the Ninth Annual 

 Meetmg of the American Phytopathological Society. (Roberts, John W. plum blotch. (Abstract.) 

 In Phytopathology, v. 8, no. 2, p. 74. 1918.) 



Journal of Agricultural Research, Vol XXII No 



Washington, D. C. Nov. i.. 1921 



^^ Key No. G-253 



70494°— 21 3 (365) 



