180 MANUAL OF FRUIT DISEASES 



BLACK-KNOT 



Caused by Plowrightia morbosa (Schw.) Sacc. 



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-INJURY 

 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.) 



DIE-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 



