356 MANUAL OF FRUIT DISEASES 



Jones, L. R. The brown rot of plums. Vermont Agr. Exp. Sta. 



Kept. 5 : 134-135. 1892. 

 Bailey, F. D. Experimental spraying of prunes for control of brown 



rot. Oregon Crop Pest and Hort. Bjenn. Kept. 1913-1914 : 241- 



244. 1915. 

 Jackson, H. S. Prune brown rot on dried fruit. Oregon Crop Pest 



and Hort. Bienn. Kept. 1913-1914 : 276-277. 1915. 

 Valleau, W. D. Varietal resistance of plums to brown rot. Journ. 



Agr. Research, 5 : 365-396. 1915. 

 (See additional references to literature on brown-rot under Peach, 



page 276, and under Cherry, page 172.) 



BLACK-KNOT 



Caused by Plowrightia morbosa (Schw.) Sacc. 



The black-knot, or plum-wart, is a conspicuous disease of the 

 plum and cherry, affecting both the wild and cultivated forms. 

 It appears that, on the whole, plums suffer more than cherries. 

 It sometimes happens that when wild plums and choke-cherries 

 are growing in close proximity, even with their branches inter- 

 mingled, the one may be affected with black-knot, whereas the 

 other shows no signs of the disease. This is explained on the 

 grounds that the pathogene has become so adapted to growth 

 on the plum, for example, that it is not capable of attacking and 

 infecting the cherry, and vice versa. There has always been 

 more or less discussion of the resistance and susceptibility of 

 various varieties, but on the whole varieties within a species do 

 not show marked differences in this respect. The Trifloras 

 are said to be affected less than any other group of plums, and the 

 Institias rank next in immunity, although the Damson is said 

 to be very susceptible. On the other hand, the Domesticas are 

 susceptible, except possibly the Middleburg and Palatine, which 

 are relatively free from black-knot. Further observations of the 

 whole question of varietal susceptibility are desirable. 



Black-knot is of native origin and has been the subject of 

 horticultural and botanical writings since the beginning of the 



