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BULLETIN 1189, U. S. DEPARTMENT OF AGRICULTURE. 



DISEASE FACTORS. 



In the descriptions of varieties of apples which are given later, the . 

 relative susceptibility of varieties to a number of diseases is often 

 given a prominent place. This is done since the disease factor in a 

 very large measure determines which varieties should be grown in 

 this area. Certain diseases seem to be more virulent in the southern 

 part of the area than in the northern part, and varieties affected by 

 those diseases are much less desirable there than farther north. 



Thus, the Ben Davis and other varieties belonging to the same 

 group, such as the Gano and Shackleford, have proved very suscep- 

 tible to the apple-blotch fungus and to the bitter and black rots in 

 Tennessee, Kentucky, and along the river valleys at the lower alti- 

 tudes in West Virginia. As a result, very few trees of this group 

 have been planted recently in the southern part of this area, and the 

 older plantings are rapidly being killed by body cankers and the 

 San Jose scale. In like manner the York Imperial, which is the 



Fig. 16. — A Grimes Golden apple orchard on Apple Pie Ridge at Gerrardstown, W. Va., 

 in the Virginia Valley and Ridge region. Orchard operations on such a site are car- 

 ried on with comparative ease. Compare with Figures 6, 7, and 8. 



leading variety in the northeastern part of West Virginia, is of little 

 value in Kentucky and Tennessee because of its susceptibility to 

 " blight." On the other hand, the Winesap and other varieties be- 

 longing to its group, such as the Arkansas, Paragon, and Kinnard, 

 'are especially adapted to the southern part of this area because they 

 are more resistant to " blight," apple blotch, and black-rot. 



Spraying, of course, will control the apple blotch and black-rot, 

 but the added cost of production makes it much more desirable to 

 plant those varieties which have proved to be the most resistant to 

 them. More than that, the cost of production, with added sprayings 

 to control these serious diseases, will be so high that the fruit from 

 such sections can not successfully compete in the general market 

 with fruit from sections where the cost of spraying is less. 



With the foregoing outline of the disease factor in mind, it will 

 be seen readily that those parts of this area which are well adapted 

 to general farming and where the land is relatively expensive will 



