PLUM DISEASES 365 



FROST-INJURY 

 Caused by the action of low temperatures 



Japanese plums behave much as do peaches when injured by 

 frost. Domestica plums, on the other hand, are more hardy, 

 except the variety Reine Claude, which is highly susceptible to 

 sun-scald. (See Apple for fuller discussion, page 35.) 



DIE-BACK 

 Caused by Valsa leucostoma Fr. var. rubescens Rolfs 



This very common disease of stone-fruits, in particular, affects 

 the plum, resulting in a dying back of the twigs and often in the 

 formation of large cankers on larger limbs. See more detailed 

 discussion under Peach, page 300. 



GUMMOSIS 



Various causal factors 



Like other stone-fruits, the plum is subject to gum-flow when 

 injured in any way. (See in this connection the discussion pre- 

 sented under Peach, page 303.) 



In the Pacific Northwest a bacterial-gummosis has recently 

 been studied, and the cause found to be Bacterium Cerasi ( = 

 Pseudom,onas Cerasus Griffin). Particular attention, however, 

 was given to it as it occurred on the cherry. The disease on 

 the plum is similar to the bacterial-gummosis of the cherry. 

 This trouble on the plum is often erroneously called winter-in- 

 jury and sun-scald, but it has been shown that in most cases at 

 least the action of the sun has nothing to do with the production 

 of this disease. Cankers similar to those on the cherry are pro- 

 duced. Such lesions on the plum, however, exude noticeably 

 less gum than those on the cherry. 



