ASCOMYCETES 



255 



Distribution. The most serious menace to grape growing in 

 most sections of the United States is the well-known black rot, 

 a fungus of American origin, the effects of which have been 

 known for considerably more than half a century. 



The black rot is now very generally distributed throughout 

 the grape-growing sections of the United States and is reckoned 

 with as a constant foe wherever susceptible varieties are grown. 

 It is supposed to have been introduced into France somewhat 

 more than twenty years ago, and it is now common in other sec- 

 tions of Europe, and throughout the Mediterranean region. Its 

 ravages are more serious under the conditions which commonly 



FIG. 109. BLACK ROT OF GRAPE, SHOWING PROGRESS OF THE DISEASE 

 (Photograph by Donald Reddick) 



encourage the growth of parasitic fungi, that is, moist, warm days, 

 or the muggy weather of midsummer, being particularly favorable 

 for its rapid development and spread. 



Symptoms. The black rot fungus occurs upon the berries and 

 leaves (Figs, no, in), also upon fruit pedicels, and sometimes 

 upon young canes. The berries are most severely affected, al- 

 though the disease may first be seen upon the leaves. Upon the 

 latter it appears as sharply defined, nearly circular, brown spots. 

 Sooner or later small pycnidia may be found at the centers of 

 these spots. The berries are not ordinarily attacked until about 

 two thirds grown. The first sign of injury is the appearance of 

 a purplish or livid brown spot, which normally spreads over the 

 whole surface of the berry. The affected fruit gradually becomes 



