8 MISC. PUBLICATION 16 8, U.S. DEPT. OF AGEICULTURE 



teristic of fruit spot. When confined to the surface region bitter 

 pit is hard to distinguish from some forms of stigmonose, except 

 for the fact that with the latter the individual corky areas are often 

 larger than most bitter-pit spots, and minute punctures can some- 

 times be seen in the skin that covers them. 



Bitter pit is a nonparasitic or physiological disease, and its oc- 

 currence is largely determined by orchard conditions.^ It is worse 

 on fruit from young trees, especially if the crop is light, than on 

 fruit from older trees, worse on large apples than on small ones, 

 and worse on apples picked immature. It is greatly increased by 

 heavy irrigation and heavy rainfall, particularly when these occur 

 late in the growing season, and by heavy nitrogen fertilization. 

 Conversely, everything that contributes to the stabilizing of mois- 

 ture conditions in the soil and to an even, normal growth of the 

 fruit throughout the season is of value in preventing the disease. 



In recent investigations in the United States and Australia, evi- 

 dence has been obtained that the disease is due to a killing of im- 

 mature starch-filled tissues of rapidly growing apples or of fruit in 

 storage, probably because of excessive transpiration that induces 

 osmotic action between the starch-filled cells and those in which most, 

 possibly all, of the starch has been changed to sugar. According to 

 this explanation the starchy areas are killed by excessive desiccation. 

 It should, therefore, be possible to reduce the amount of bitter pit by 

 speeding up the rate of ripening. In a recent series of tests (3) 

 it has been found that although the development of bitter pit is re- 

 tarded by storage at 32° F., it will develop rapidly on immature fruit 

 after removal from such storage. On fruit held continuously at 70° 

 after harvest the disease made less development than on fruit held 

 at lower temperatures, which did not permit as rapid ripening. 



Bitter pit does not spread from one apple to another in transit or 

 in storage, but under favorable conditions (see above) spots already 

 present may enlarge and others may develop either on fruit affected 

 when stored or on seemingly sound apples from the same orchard or 

 similar orchard conditions. {3, 22, 25, 32, 33, 3If, 35, 62, 72, 75, 80, 100, 

 105, lU, 133, 153, 15i, 156, 156, 157, 169, 175, 186, 195, W8, ^09.) 



BITTER ROT 



(Glomerella cingulafa (Ston.) Spauld. and Schrenk) 

 OCCURRENCE, SYMPTOMS, AND EFFECTS 



Bitter rot is of greatest importance on the apple, though it may 

 occur on pear, peach, quince, and cherry. It is found in practically 

 all apple-growing regions east of the Great Plains, but it is most 

 common and most destructive in a strip of territory extending from 

 Arkansas and southern Missouri eastward to North Carolina and 

 Virginia. Even there it is irregular in occurrence, being worse in 

 warm, wet weather than in dry and fairly cool weather. 



The disease usually appears in the orchard in late June or early 

 July but becomes most serious in August and September on well- 

 developed fruit, hence the name '' ripe rot " sometimes applied to it. 



