GRAPE DISEASES 



233 



volved. After about a week the berry is a hard and shriveled 

 mummy (Fig. 59). 



Although the berries, of all susceptible parts of the vine, are 

 most severely affected, the disease may first be observed on the 

 leaves (Fig. 60) . In June or early in July black-rot appears on 



the leaves in the r ____ 



form of reddish 

 brown, somewhat 

 circular spots. 

 Close observa- 

 tions show that 

 the first evidence 

 of the trouble on 

 the leaves is a 

 slight blanching 

 of the affected tis- 

 sue. The small 

 veinlets form the 

 margin of the spot 

 so that, while the 

 shape of the le- 

 sion tends to be 

 circular, the out- 

 line is finely cren- 

 ulate (Fig. 60). 

 Soon the center 



of the affected FIQ 6Q _ Black _ rot i es i ns on grape-leaf. 



area becomes 



ashen-gray, but at this stage the margin is still brown. By 

 the time the spot is just visible to the unaided eye the 

 margin appears as a black line. Two or more spots may coalesce 

 to form large irregular areas. The fruiting bodies of the patho- 

 gene protrude through the cuticle of the leaf. These structures 

 are black and are arranged promiscuously or in more or less 

 concentric rings (Fig. 60). 



