Diseases of the Plum 335 



not heal for a long time. Often it never does. The 

 diseased portion seems rather to increase in area. The 

 margins are raised, blackened, with a hard, scaly sur- 

 face. In the middle of such a wound will often be 

 found the dead stub of the branch from which the trou- 

 ble started. A better idea of the appearance of this 

 canker may be gained from the accompanying illus- 

 stration, p. 334. This trouble, which is occasionally 

 serious with peaches, does not seem to be so common 

 with plums. The worst cases that I have observed 

 were on Satsuma trees. 



The Japanese varieties are undoubtedly the most 

 susceptible. The Americana species all have harder, 

 tougher, closer-grained wood, less subject to mechan- 

 ical injury and less subject to gummosis. Still, I have 

 observed incipient cases of the canker here described 

 on trees of Whitaker, Strawberry and a few other na- 

 tive sorts. In some instances the branches are so much 

 weakened by this canker that they break off readily in 

 the wind or under moderate loads of fruit. This com- 

 pletes the chain of troubles; monilia, gummosis, can- 

 ker, breakdown. 



Gummosis is apparently always a secondary mat- 

 ter. The way to treat it, then, is to get at the primary 

 cause. If due to borers, apply the remedy for borers. 

 If due to overbearing, thin the fruit. If due to bruises 

 from the single-tree, discharge the hired man. If due 

 to monilia, spray. The last is perhaps the most impor- 

 tant cause and the most practical remedy. 



Curl-leaf, or Sunburn. These have been de- 

 scribed as separate troubles; but they appear to be 

 closely related, if not identical. The curl-leaf has been 

 described by Hedrick,* who found it characteristic 

 of the Italian Prune in Oregon and other parts of the 



*U. P. Hedrick, Oregon Experiment station Bulletin 45:72. 1897. 



