158 



MANUAL OF FRUIT DISEASES 



attempt to distinguish the two die-back diseases. Where 

 Valsa leucostoma var. rubescens is a factor, its pycnidia show as 

 whitish dots over the surface of the lesion. 



(See in this connection Frost-Injury under Apple, page 35, 

 and Die-Back under Peach, page 299.) 



BLACK-SPOT 

 Caused by Bacterium Pruni E. F. Smith 



As a rule, apricot fruits are less injured by black-spot than 

 those of the other susceptible stone-fruits like the peach and 



plum. However, certain 

 varieties of apricots are 

 severely affected; the 

 Royal, Sweet Russian, 

 Peach and Bread va- 

 rieties are prominent in 

 this respect. 



The disease is also found 

 on the twigs, where it 

 shows as black spots, 

 but these, as in the 

 case of those on nec- 

 tarine twigs, disappear, 

 and open cankers develop 

 to some extent. On the 



FIG. 44. Black-spot on apricot leaf. 



leaves a shot-hole effect is found subsequent to a dying of small 

 areas (Fig. 44). (See Peach, page 306.) 



SILVER-LEAF 

 Caused by Stereum purpureum Fries 



The apricot is not infrequently affected by silver-leaf. The 

 diseased trees are recognized by the peculiar ashen-gray color 



