SOME OF OUR MOST COMMON APPLE DISEASES 



II. II. \YlIETZEL 

 Professor of Plant Pathology, Cornell University, Ithaca, N. Y. 



and 



LKX K. HKSLEU 

 Assistant Professor of Plant Pathology, Cornell University, Ithaca, X. Y. 



Al'l'LK S< AH 



The scab disease of apples, which is 

 caused by the fungus, Ventupiaincequcdis } 

 is by far the most common and destruc- 

 tive disease of this fruit in New York 

 State. The nature of the losses incurred 

 explains in a large degree why the trouble 

 is so serious. Ordinarily the reduction 

 in quality of the fruit due to this disease 

 is considered to be the main source of the 

 loss. While this is important, it consti- 

 tutes only one of the several factors involved. 



In some years, as for example in 1910, early scab infection, 

 when not controlled, a'most wholly prevents the setting of fruit. 

 On the other hand, where a fine set of fruit occurs, the apples 

 are liable to infections during all stages of development. In case 

 a. single lesion appears on a young apple, its growth on the affected 

 side is retarded and there results an unsymmetrical fruit. Fre- 

 quently fifty to seventy-five per cent of the apples are scabby, 

 which means little or no returns for such fruit at picking time. 

 Fruit thus affected does not keep so well in storage, the scab spots 

 furnishing an easy entrance for storage-rot organisms, such as 

 the pink-rot fungus. 



In addition to the immediate effect on the crop of the current 

 year there is, in case of severe leaf infection, a devitalizing effect 

 <>M the tree. Reliable figures on losses from this disease are very 

 difficult to obtain. Such figures are to be obtained only by esti- 

 mates based upon increased profits from sprayed orchards. Since 

 such returns almost invariably include not only saving from scab, 



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