PEACH DISEASES 295 



does not cause injury sufficient to make spraying for its control 

 a profitable or necessary operation. 



Symptoms. 



The fruits, leaves and twigs are affected. On the fruit 

 (Fig. 78) small, round, olive-black spots begin to show about 

 six weeks after the blossoms fall, or from June 15 until July 10, 

 depending on the variety. Lesions most frequently occur on 

 the upper side of the fruit. If the spots are numerous, they 

 coalesce, forming a large, irregular diseased area covering a 

 greater portion of the fruit's surface (Fig. 78) and preventing 

 the normal expansion of the skin as well as interfering with 



FIG. 78. Peach-scab ; types of lesions on the fruit. 



the ripening and mellowing of the flesh. The fruit often be- 

 comes one-sided, due to a formation of a protective cork-layer 

 under the diseased area. This layer is incapable of further 

 growth, and hence an ill-formed fruit results. Often the cork- 

 layer is ruptured, leaving deep cracks (Fig. 78) through which 

 the brown-rot pathogene enters (see page 275). Attacks are 

 generally most noticeable on the late varieties, due, in part 

 perhaps, to the fact that the fruit of such varieties is exposed to 

 infection over a longer period. Of the commercial varieties, the 

 Heath is said to be most susceptible. The Bilyen and Hill's 

 Chili are also badly affected, and the Sal way, Smock and Morris' 

 White suffer severely. The Elberta is sometimes badly dis- 

 eased, but is more resistant than those just mentioned. The 

 Carman, Hiley, Champion and Belle are slightly affected. Trees 



