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



terials. Being abundant in the orchard, the spores are present on 

 the fruit when it is harvested. A. tenuis is a weak parasite, which 

 does not cause decay unless the apples have been injured or weak- 

 ened. It has been observed growing and producing spores on the 

 calyx sepals of apples without causing rot. 



Under favorable conditions the rot may occur on apples from 

 all producing sections. During the long period of storage the rot 

 develops proportionately with the type of injury permitting its 

 entry and with the vitality of the apple. Where the injury is 

 slight and the apple firm alternaria rot is characterized by small, 

 firm, slightly sunken lesions, which may be brown around the 

 edges but are covered for the most part by a rough, black crust. 

 When apples are removed from storage these spots may enlarge 

 and produce larger rotted areas, which may be brown or grayish. 



Alternaria rot often develops by midseason in cold storage on 

 apples showing injuries such as delayed sunscald (pi. 5, F), 

 bruising, or chemical injury. In apples held late in storage the 

 rot may develop at skin checks, as in the York Imperial variety, 

 or even at enlarged, ruptured lenticels over bruises. 



The rot lesions are more or less round, and when less than 1 

 inch in diameter they resemble side rot in color and appearance 

 (pi. 5, E). They are, however, firm, with fairly tough skin, 

 whereas tissue affected with side rot gives readily under pres- 

 sure and the skin is tender. The spots are brown when small, but 

 generally become black as they develop. 



Alternaria infections frequently follow the death of the skin 

 and tissue as a result of scald, soft scald, or Jonathan spot. The 

 lesions are usually black, not sunken, and often without definite 

 margins. A similar rot is produced by Cladosporium herbarum 

 Fr., a very weak parasite, on killed apple tissue. It is inadvisable 

 to attempt to distinguish the two without laboratory study. The 

 most practical procedure is to describe the condition as a sec- 

 ondary, undetermined black rot following scald, soft scald, or 

 other diseases as the case may be. 



Certain other rots may be confused with alternaria rot, but 

 they can usually be differentiated by careful examination. Black 

 rot is distinguished from alternaria rot by the presence of either 

 alternating zones of light and dark brown or black pimplelike 

 fruiting bodies (pycnidia). Brown rot is usually not sunken, 

 may have black spots at the lenticels and, when it becomes uni- 

 formly black, has a velvety sheen. Bitter rot can be differentiated 

 from alternaria rot by its brown color and sometimes by the 

 presence of wet pink or cream-colored spore masses, which may 

 be in concentric rings. 



Alternaria rot does not spread from one fruit to another by 

 contact either in storage or in transit. 



CONTROL MEASURES 



Control of alternaria rot depends upon careful handling during 

 picking, washing, and packing and on the prevention of physio- 

 logical diseases and injuries which open the way for infection. 

 Prompt storage and cooling of the fruit are of primary impor- 

 tance. Removal of apples from cold storage to warmer tempera- 

 tures favors the development of the rot. Consequently moving 



