194 MANUAL OF FRUIT DISEASES 



it is an accompanying characteristic of cranberry-rot (see 

 page 201). 



When the flowers are affected, they suddenly shrivel and die. 

 This effect is commonly known as blast. 



Leaves are not usually affected, but do not always escape. 

 Brown spots, irregular in outline, are produced at times. Within 

 such areas the black fruiting bodies of the pathogene may be 

 found. Ultimately the leaves turn yellow and fall. 



Cause. 



Cranberry-scald is caused by the fungus Guignardia Vac- 

 cinii. It was formerly held that it is caused by too much acid 

 in the soil. It was also believed that excessive heat and drought 

 are contributing factors which induced fermentation in the 

 fruit. A condition similar to scald is sometimes induced when 

 berries are flooded and kept covered with water for a half day 

 or more during hot weather. 



The causal fungus, Guignardia Vaccinii, is found generally 

 in the cranberry sections of the country. It was once thought 

 that it lived perennially in the stems, and that it entered the 

 fruit therefrom. But now this is regarded as a false idea. 

 The fungus winters in the old fallen leaves. In the spring 

 pycnospores initiate the first infections. The time and manner 

 of this process is unknown. But it seems very likely that 

 it occurs very early in the growing-season, soon after the water 

 is removed from the bog, and while the berries and leaves are 

 quite young. Assuming that pycnospores from old leaves 

 come to lie on the susceptible parts, then, under conditions 

 favorable to the process of germination, a germtube is developed 

 from each spore. The organ inoculated is penetrated and a 

 mycelium is developed. It appears that after the fungus has 

 entered its host it may remain inactive for some time, during 

 which period there is no external evidence of the disease or 

 the fungus. Thus affected berries may pass unnoticed as 

 healthy fruit. The conditions affecting the length of this 



