CERTAIN ELEMENTS IN NURSERY PRACTICE 201 



is often the chief cause of the dropping of currant leaves and 

 may be destructive also on gooseberries. 



Description. The septoria leaf-spot disease causes rather 

 large angular lesions with grayish centers and brown borders. 

 Within the grayish center of old spots may be observed several 

 minute black specks. The spots may be few or many on the 

 leaf; when they are numerous, the leaf turns yellow and falls 

 prematurely (Figs. 215, 

 216). The septoria 

 leaf-spot is distin- 

 guished easily from the 

 anthracnose disease by 

 the much .larger and 

 well-defined lesions, 

 with characteristic 

 light-colored centers. 



Cause. The dis- 

 ease is caused by the 

 fungus Mycospk&rella 

 grossularice. The mi- 

 nute black specks in 

 the center of the old FIG. 

 spots are fruiting 

 bodies (pycnidia) of the fungus. The pycnidia contain spores 

 which are disseminated by the wind and rain, and are thus a 

 means for further spread of the fungus. Falling on currant or 

 gooseberry leaves, the spores germinate and produce new in- 

 fections. The fungus lives over winter in the old leaves on 

 the ground and in the spring special spores are produced that 

 attack the new foliage. As with most leaf-spot fungi, heavy 

 rains, followed by damp cloudy weather, greatly augment 

 the spread of this parasite. 



Control. Measures suitable for the anthracnose disease 

 control also the septoria leaf-spot. The first application 



216. 



Saptoria leaf-spot of currant and 

 gooseberry. 



