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 Ralfs 
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 paces 
been studied, and the cause found to be Bacterium Cerasi (= 
Pseudomonas 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. 
