MAEKET DISEASES OF APPLES, PEARS, QUINCES 9 



The most susceptible varieties are Yellow Newtown, Huntsman, Wil- 

 lowtwig, and Ben Davis. In Arkansas and southern Missouri, 

 Jonathan and even Winesap are sometimes affected. 



Bitter rot is characterized by brown, definitely limited spots 

 varying in size from mere specks to lesions involving the whole 

 side of an apple (pi. 1, C). In extreme cases the entire fruit may 

 be rotted. Spots smaller than one eighth of an inch in diameter — 

 not common on the market — usually occur as green or brown blister- 

 like areas that are dry and firm. Larger spots are sunken and soft. 

 Contrary to the implication in the name " bitter rot ", the decayed 

 flesh is not generally bitter. Spots half an inch in diameter or 

 larger usually show spore masses that may or may not be arranged 

 in concentric circles. Under orchard conditions these spore masses 

 are at first pink or cream colored; eventually they become gray 

 or almost black. In storage they may not show the pink color 

 at any time. The color and arrangement of the spore masses serve 

 to distinguish the disease from black rot, in which the pycnidia 

 (spore-producing bodies) are always black and scattered irregu- 

 larly over the diseased area. The alternating zones of light and 

 dark brown so characteristic of black rot are rarely seen in bitter 

 rot except in affected apples held in storage for some time. 



CAUSAL FACTORS 



The disease is spread by means of spores, which are produced in 

 immense numbers during the growing season on bitter-rot mummies 

 of the preceding year, on cankers caused by the bitter-rot fungus 

 {Glomerella cingulata) ^ and on blight, black rot, and other cankers 

 at the edges of which the bitter-rot fungus has established itself. 

 In warm wet weather the spores are washed down on the apples 

 below and germinate there, producing fungus threads which enter 

 the fruit and cause decay. 



Bitter-rot cankers consist of sunken areas of dead bark, usually 

 somewhat oval in outline, beneath which the wood is dead and 

 dry {191). The dead bark adheres rather firmly to the wood and in 

 older cankers frequently has a zoned appearance because of the 

 development of cracks parallel to the edges of the canker. Often 

 the canker is surrounded by a layer of callus, which prevents its 

 further extension and eventually obliterates it entirely. 



CONTROL MEASURES 



Bitter rot is rarely seen on the market. It probably develops to 

 some extent after picking on fruits already infected, if the tempera- 

 ture is not kept below 50° F. Apparently it does not spread from 

 one fruit to another. 



Control measures include frequent thorough spraying with 4-4-50 

 Bordeaux mixture, beginning about the middle of June, the removal 

 of cankered limbs, the scraping and painting of cankers, and the 

 removal of bitter-rot mummies. {11, 22, 75, 100, UJf, 118, 119, 183, 

 187, 189, 190, 191, 193, 195, 201, 203, 204, ^08, 209.) 



