356 MANUAL OF FRUIT DISEASES 
Jones, L. R. The brown rot of plums. Vermont Agr. Exp. Sta. 
Rept. 5: 134-135. 1892. 
Bailey, F. D. Experimental spraying of prunes for control of brown 
rot. Oregon Crop Pest and Hort. Bienn. Rept. 1913-1914 : 241— 
244. 1915. 
Jackson, H. S. Prune brown rot on dried fruit. Oregon Crop Pest 
and Hort. Bienn. Rept. 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.) 
BiLackK-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 
