28 MISC. PUBLICATION 168, U. S. DEPT. OF AGRICULTURE 



and Rhode Island Greening internal cork predominates and the 

 surface of the apple remains normal. Wealthy, Mcintosh, Olden- 

 burg (Duchess), and Northern Spy usually have both external and 

 internal cork. Regardless of variety, when the disease develops 8 

 weeks or more after petal fall cork is usually entirely internal. In 

 some varieties the internal cork spots are accompanied by certain 

 external symptoms, less severe and of a different character than 

 those described for external cork. In other varieties there are no 

 external signs of the disease. 



It is sometimes difficult to distinguish mild surface cork, bitter 

 pit, and stigmonose, because each may have as a symptom a corky 

 spot immediately below a surface depression. It is safest to 

 diagnose a disorder as cork only when additional corky spots are 

 located deep in the flesh near the core. The diagnosis can be made 

 with assurance if the spots are confined to the stem end of the 

 apple. 



The ordinary type of bitter pit, with relatively small pits — 

 often in considerable numbers — located around the calyx end of 

 the fruit, is readily recognized. The pits and the corky spots are 

 smaller than the surface depressions and corky spots associated 

 with cork. Like cork spots, however, bitter pit spots are associated 

 with the vascular bundles. 



When bitter pits occur deep in the flesh it is much more likely 

 to be confused with cork, especially if the surface depressions and 

 corky spots are larger and fewer in number than when bitter pit 

 occurs at the surface. The disorder would be recognized as bitter 

 pit rather than cork if the spots are more or less confined to the 

 calyx end and do not occur around the core. 



Internal cork spots adjacent to the peel and beneath surface 

 depressions are very similar to stigmonose. The two disorders 

 may occur on the same fruit. Spots of corky tissue adjacent to 

 the peel and in conjunction with flattened or broadly depressed 

 surface spots occurring anywhere on the fruit, with no cork spots 

 deeper in the flesh, are most likely to be stigmonose (pi. 4, G, H). 



Besides the surface depressions similar to stigmonose, there 

 are other surface characteristics that may accompany internal 

 cork. Some varieties show dimplelike depressions, and in others 

 the surface is pebbly, lumpy, or corrugated. It is thought that 

 the stage of development of the fruit when the disease starts 

 affects the occurrence and extent of external symptoms accom- 

 panying internal cork. Perhaps most varieties show some ex- 

 ternal symptoms in severe cases. Because of the nature and 

 complexity of the disorder, however, it is best to make a diagnosis 

 from the location of internal cork spots rather than from the 

 external characteristics. 



Diseases of the cork type are widely distributed. They have 

 been reported from all the important apple districts of Wash- 

 ington and Oregon, from New York, from various apple districts 

 of Virginia and West Virginia, and from British Columbia and 

 New Zealand. The trouble known in California as hollow apple 

 seems to be very closely related to cork. 



In New York, Cortland, Mcintosh, Fameuse, Oldenburg, and 

 Ben Davis are among the varieties most severely affected. Wealthy 

 is moderately affected ; and Baldwin, Northern Spy, Jonathan, 



