FUNGI AFFECTING THE GRAPE 



The Black Rot 



Lcestadia bidivellii 



This is the most generally destructive fungous dis- 

 ease of the grape in the United States. It is most inju- 

 rious in southern latitudes, being much less yirulent as 

 far north as Northern Ohio or Western New York than 

 in Tennessee or the Carolinas. Like most fungous dis- 

 eases, it develops with greatest rapidity during damp, 

 hot weather, or when nights with heavy dews alternate 

 with hot days. 



The black rot fungus usually first appears on the 

 leaves early in summer in the shape of small, sharply 

 defined reddish-brown spots, having yellowish centers, 

 and dark brown or blackish borders, with numerous 

 minute black pustules scattered over the surface. A 

 short time afterward — generally about a fortnight — the 

 attack upon the fruit becomes noticeable. 



According to Professor F. D. Chester, who has 

 studied tins disease in Delaware, ^'^the first appearance 

 of rot upon the berry shows itself as a light brown spot, 

 caused by the decay of the underlying pulp, this spot 

 increasing in size so as to involve the entire berry. 

 Simultaneous with this change, the parts first affected 

 turn black and become covered with minute black pus- 

 tules. Finally the entire berry dries and shrivels, the 

 skin crumpling into angular folds. The entire berry is, 

 at this stage, profusely and uniformly covered with the 

 pustules. If a thin section be made through a rotting 

 berry, the microscope will reveal the presence of minute 



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