BLACK ROT OF GRAPES 105 



BLACK ROT OF GRAPES 

 (Guignardia bidwellii, Viala and Ravaz.) 



This fungus is probably the most destructive and wide- 

 spread of enemies against which viticulturalists in the 

 United States have to cope. The disease was introduced 

 into Europe along with vines imported from North 

 America to replace those destroyed by the Phylloxera, 

 itself a pest of American origin, being first observed in 

 France by Professor Viala in 1885. 



During certain seasons the crop of grapes is much 

 injured in this country ; and when once established, it is 

 only by exercising the greatest amount of promptitude and 

 cleanliness that the fungus can be exterminated. As a rule, 

 young shoots and leaves are first attacked, the disease 

 appearing under the form of small brownish patches, 

 somewhat resembling the blotches caused by sun-scald. 

 About a fortnight later, the fruit shows symptoms of 

 disease ; small blackish or brownish spots appear at 

 different points on the surface ; very soon the fruit becomes 

 black, shrivelled, and hard, but as a rule does not drop 

 off. If examined with a pocket lens at this stage, the 

 surface of the patches will be seen to be studded with 

 minute black points. These points are pycnidia or summer 

 fruits, which produce innumerable minute bodies called 

 stylospores or reproductive bodies in their interior. The 

 stylospores ooze out of a small opening at the top of the 

 pycnidia in the form of slender threads, being held together 

 by a sticky substance ; they are however readily separated 

 by dew or rain, and those that happen to be carried on to 

 the surface of a damp grape germinate at once, enter the 

 tissues, and soon give origin to a diseased spot, which in 

 course of time produces more stylospores. 



