SPREAD OF BITTER ROT. 37 



One apple grower carefully marked the trees which were affected with 

 bitter rot in 1900. When the rot first appeared in his orchard in 1902 

 (there was hardly any rot in 1901) he went over the orchard and found 

 that every tree marked in 1900 had bitter rot, and not only that, but 

 that the rot was at first confined to these trees. 



Another observation frequently recorded is that the disease often 

 starts on a few trees and, starting from this center, it gradually 

 spreads year after year and finally affects the entire orchard. Mr. J. W. 

 Beach, of Batavia, Ark., stated a typical case: 



I came to this country in 1884, and that season there were four trees in my old 

 orchard affected. * * * For the last three years the disease has steadily increased, 

 so that this year (1887) my old orchard of seventy-live trees will not yield 25 bushels 

 of sound apples. 



This apparently erratic behavior of the bitter rot can be explained 

 in part since the discovery of the canker stage of the fungus. After 

 its introduction into an orchard or on one tree the fungus attacks one 

 or more branches, probably early in the summer, and produces a 

 canker. The next year the spores from this canker will be washed 

 down on the ripening fruit b}^ a rain. The water is sprayed from 

 the branch on which the canker is situated to the lower branches in 

 the form of a cone, and one or more spores will probably fall on every 

 apple within such a cone. 



The presence of the winter stage of the fungus will explain why 

 the rot is apt to recur on the trees affected the year before with the 

 bitter rot, and also why the disease should first appear on such trees. 

 The cankers produce spores early in the season, and from the trees 

 which have cankers the disease spreads to neighboring trees. 



The bitter rot is apt to appear in virulent form only once in two or 

 three years. During the intervening periods there may be little or no 

 rot in any one region. This may possibly be caused by weather con- 

 ditions generally unfavorable to the fungus, as was the case in the 

 summer of 1901, but it may also be due to conditions unfavorable to 

 the growth of the fungus in the cankers. 



The exact conditions which favor the development of the bitter-rot 

 fungus on the branches are not known as yet, but it is conceivable that 

 these might be such as would retard its growth in the canker to such 

 an extent that few or no spores would be found during one year. 



That the spores of the bitter-rot fungus are spread to the fruit from 

 the cankers in the tree now seems proved beyond doubt. The dissemi- 

 nation of spores from the cankers probably begins early in summer 

 and continues until the apples are fully grown. 



Another source of infection is found in the dried mummies hanging 

 on the trees and lying on the ground under the trees. The diseased 

 apples of one season either fall to the ground (which most of them do) 

 or they remain on the trees, where they dry and shrivel up. When 



