316 MANUAL OF FRUIT DISEASES 
Only young growing twigs are affected. Conspicuous 
white patches appear on the surface. The bark becomes 
dry and brown at infected points, and in severe cases the 
leaves fall as a result. Finally the bark shrivels and the 
young tips become 
curved; growth is 
thus checked and 
the twigs may die. 
The disease may 
involve the whole 
or, more commonly, 
only a portion of 
the fruit. It ap- 
pears as a frost- 
like covering which 
assumes a pure 
white aspect due 
to the presence of 
the mildew-patho- 
gene (Fig. 84). 
The affected peach 
flesh hardens and 
the skin turns brown, and finally the peach cracks. Young 
fruits are often caused to fall prematurely. 
| In Oregon two types of symptoms have been noted: (1) 
mildew scattered on the fruit and leaves, twigs less affected ; 
(2) general on all parts. The former is thought to be the true 
peach-mildew disease; the latter the cherry-mildew (see page 
177). 
Cause. 
The name of this powdery-mildew organism is Spherotheca 
pannosa var. Persice. Its mycelium grows in dense superficial 
patches, giving to the lesions the powdery-mildew aspect already 
described. Soon after the fungus appears, great numbers 
Fic. 83. — Peach-mildew on shoots and leaves. 
