CHAPTER XVI 

 DISEASES OF THE GROSELLES 



MANY fungi are known to attack the genus Ribes, yet 

 few do harm enough to demand consideration from an 

 economic stand point. The one which is best known, and 

 which has created far more discussion than any other in 

 American horticultural literature, is the gooseberry mil- 

 dew. This disease alone, like the phylloxera of the grape, 

 has forced the development of varieties from native species, 

 which doubtless would not have been done had the Eng- 

 lish varieties proved successful in this climate. The fol- 

 lowing list includes those diseases which are most im- 

 portant. 



GOOSEBERRY MILDEW 



Spcerotheca mors-uvce, Schw., B. and C. 



This is one of the most widely known of the diseases affecting the 

 genus Ribes. It first appears on the young leaves and tender tips 

 of the growing shoots. The young fruits are soon attacked in the 

 same way and partially or entirely checked in their growth, being 

 rendered wholly unfit for use in most cases. It first appears as a 

 patch of cobweb-like threads, which soon form a dense mat and 

 become white and powdery from the development of white conidial 

 or summer spores. These are produced in immense numbers, and 

 are readily blown about by the wind, or carried by rain, to contribute 

 to the further spread of the disease. A few weeks later the winter 

 spores, or ascospores, begin to develop. These are contained within 

 chestnut-colored perithecia, which give a dirty brown appearance 



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