Small Fruits 117 



colored powder appears upon the lower surface of the leaves 

 of currants and gooseberries accompanied by but slight dam- 

 age. The spring stage occurs upon trunks and branches of 

 the white pine, and is there very destructive. For history, 

 distribution, and general discussion, see pine. 



Minor diseases 



Powdery-mildew, see gooseberry; Root-rots due to Armil- 

 laria, see apple, to Fomes ribis (Schw.) Fr., see gooseberry; 

 Silver-leaf, see plum ; Cluster-cup-rust, see gooseberry. 



DEWBERRY. See blackberry. 



GOOSEBERRY i^" 



Powdery-mildew ^^^ (Sphcerotheca mors-uvce (Schw.) B. & 

 C). — This disease appears to be of American origin, 

 whence it invaded Europe, appearing first in Russia in 1890 

 and in Ireland about 1900. It is now general in Europe 

 where it is much more destructive than here. The mildewed 

 appearance of the leaves, stems, and fruit, all of which appear 

 whitened as though dusted with flour, is characteristic. 

 Close inspection shows each blotch to consist of cobwebby 

 threads densely matted in the central portions of the 

 spot. Later these blotches turn brown, blend irregularly 

 into fewer spots, and form large diseased areas. As the 

 spot ages, its threads weave together into a thick brown- 

 ish felt. 



The young leaves and growing parts are robbed of nourish- 

 ment, and thus their growth is checked, resulting in serious 

 injury. The berries, if subjected to one-sided attack, become 

 deformed and curved, owing to the retarded growth of the 

 diseased side. They often crack open and decay. Diseased 

 leaves turn brown. Toward the completion of the season's 

 growth small, nearly microscopic, Ijlack perithecia are pro- 

 duced in the centers of the diseased spots. 



The damage caused by powdery-mildew is excessive and 

 presents the most serious obstacle to the successful culture 



