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 
leaves a shot-hole effect is found subsequent to a dying of small 
areas (Fig. 44). (See Peach, page 306.) 
Fic. 44. — Black-spot on apricot leaf. 
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 
