180 MANUAL OF FRUIT DISEASES 
Biack-Knot 
Caused by Plowrightia morbosa (Schw.) Sace. 
Black-knot is perhaps the most conspicuous disease of 
cherries. It is common also to plums; in fact, plums suffer 
more from this disease than do cherries. However, cherries 
of many varieties are affected with black-knot, including choke- 
cherry, wild black or rum-cherry, bird or pin-cherry, and 
morello varieties. Sweet cherries are said to be much less 
affected than sours. The English Morello, the standard late 
sour cherry of North America, probably suffers as much as 
any of the cherries. At times serious injury is inflicted on this 
and other varieties, particularly in the eastern United States. 
In North Carolina, for example, cherry-growing was abandoned 
in 1906 because of black-knot injury. The disease also occurs 
in the West. (For fuller discussion of symptoms, cause and 
control, see Plum, page 356.) 
Frost-INJuryY 
Caused by the action of low temperatures 
Cherries are injured more or less every year by frost in locali- 
ties away from large bodies of water. The sweet varieties are 
particularly susceptible to frost-injury, although sour cherries 
are affected. Gum exudes from the injured bark in early 
summer, and on cutting into such places large gum-pockets 
are revealed. (For fuller discussion, see Apple, page 35.) 
Drir-Back 
Caused by Valsa leucostoma Fr. var. cincta Rolfs 
This disease is common on stone- and pome-fruits everywhere. 
Considerable difficulty has been experienced in some sections 
