162 



DISEASES OF ECONOMIC PLANTS 



about 3-8 mm. in diameter, many or few 

 according to the severity of the infection. 

 In or near the centers of the older spots 

 upon the upper surface of the leaves are 

 seen' the nearly microccopic pycnidia 

 which are often arranged in concentric 

 circles. 



On the young shoots the spots are some- 

 what more reddish and are often craclced 

 longitudinally, but otherwise they are as 

 upon the leaves. 

 I This rot is much worse in warm, hiunid 



^ weather than in dry times, and a few days 

 g of muggy weather may so favor the 

 g growth of the causal fungus as to develop 

 g an epidemic, which may in turn be 

 I checked by a dry spell. Often the dis- 

 "^ ease appears in distinct waves during the 

 season, each wave corresponding to a 

 climatic condition favorable to infection 

 and usually lagging behind such favor- 

 able condition a period of 8 to 14 days, 

 the time necessary after infection for the 

 disease to become conspicuous enough to 

 /i^^^^^\ I attract the attention of the vineyard- 



^l^^H^P'l S ist. The first infections of each season 

 ^^^^^' 2 occur upon the stem, leaf, petioles, and 

 tendrils. 

 While the Scuppernong occasionally shows a few spots 

 upon leaf or berry and the blossom is sometimes affected, 

 this variety is practically immune. 



