204 



MANUAL OF FRUIT DISEASES 



seasons nearly complete defoliation occurs. This loss of foliage 

 interferes with the maturing of both the wood and buds, 

 and as a result the succeeding crop is injured. Perhaps the 

 cumulative effects constitute .the worst feature. 

 Symptoms. 



During the month of June, lesions appear as small brown 

 spots (Fig. 53) on the upper and lower surfaces of the leaves. 



The spots may number few 

 or several to a leaf. Each dis- 

 eased area enlarges until it 

 has reached a diameter of 

 about one-eighth of an inch, 

 and the center becomes pale 

 with small black fruiting 

 bodies of the pathogene, while 

 the border remains brown 

 (Fig. 53). Older lesions are 

 frequently confluent. From 

 the last of June to August 

 the affected leaves turn yel- 

 low and fall prematurely. 

 This happens on red and white 

 currants particularly. The 



leaf-spot lesions are distinguished from those of the anthrac- 

 nose by their larger size, sharp outline, and pale, dead center. 

 Cause. 



The causal organism, Mycosphcerella Grossularice, is a fungus 

 which has been known since 1842. It was first described from 

 Europe. When the affected leaves fall to the ground, the fungus 

 is carried with them. It begins to develop perithecia, but these 

 do not reach maturity before winter comes. With the advent 

 of spring these bodies complete their growth. Within each 

 many ascospores are formed. These are discharged with force 

 into the air, are caught by the air currents, and are carried to 



FIG. 53. Mycosphaerella leaf-spot 

 on currant. 



