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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 Sphcerotheca 

 pannosa var. Persicce. Its mycelium grows in dense superficial 

 patches, giving to the lesions the powdery-mildew aspect already 

 described. Soon after the fungus appears, great numbers 



FIG. 83. Peach-mildew on shoots and leaves. 



