160 DISEASES OF ECONOMIC PLANTS 



shown in the left figure gives decidedly better results than 

 when the spraying is delayed until the condition shown in 

 the other two figures. 



Black knot. See currant. 



Anthracnose. See currant. 



Septoriose, leaf spot. See currant. 



Cercosporose, leaf spot. See currant. 



Cluster cup (Pucdnia Grossularias (Schum.) Lagerh.). — 

 Occasionally reddish swollen or thickened spots are no- 

 ticed over the leaves and sometimes upon the fruit. 

 Close examination shows each spot to consist of a clus- 

 ter of minute cups embedded in the tissue of the leaf, 

 whence the name "cluster cup." With a lens each cup is 

 seen to consist of a fringed rim extending above the surface 

 of the leaf, and to be filled with very small red spores. 



The winter condition is found upon quite different plants; 

 namely, various common sedges, upon the leaves of which 

 it constitutes a genuine rust. 



The damage from this disease is not serious, and no experi- 

 ments on a large scale, in prevention, have been undertaken. 

 If it should prove destructive, thorough eradication of the 

 sedges in the neighborhood, particularly any that are 

 rusted in autumn, would be deemed necessary. 



Root rot (Dematophora sp.). — Root rot upon both 

 the gooseberry and currant has been reported from some 

 states. 



The plants die slowly. T\Tien dead and living canes are 

 found in the same hill, the living canes are somewhat 

 dwarfed. The disease apparently spreads through the 

 soil, and the diseased soil area enlarges year by year. Upon 

 roots of diseased plants there are conspicuous white threads, 



