426 MANUAL OF FRUIT DISEASES 



worthless. Affected fruit dries up and neither colors nor 

 matures. Its surface becomes covered with powdery-mildew, 

 as described for the leaves. The fruiting-stalks are also 

 affected. 



Cause. 



The causal fungus, Sphcerotheca Humuli, grows superficially 

 on the various organs of the strawberry plant. The powdery- 

 mildew growth is composed of mycelium, conidiophores and 

 conidia. At frequent intervals the mycelium sends haustoria 

 into the epidermal cells for the purpose of obtaining food. As a 

 result of this drain, the leaves curl and the plant suffers generally. 

 The conidia produced on the leaves are blown to other plants, 

 and infection may result. It is held by some that this same 

 fungus attacks hops. Others believe that while the fungi 

 on hops and strawberries are alike in form and structure, they 

 will not pass back and forth, that is, the fungus on hops can- 

 not infect the strawberry, and vice versa. This point needs 

 further study. Later in the summer the pathogene develops 

 perithecia. These are formed in the mycelial mats on the 

 surface of the fruit, on the leaf -blades and leaf-petioles. These 

 bodies carry the fungus through the winter. In the spring, 

 ascospores are liberated and are carried to the growing plants, 

 where infection results. 



Control. 



Little is known about the control of strawberry-mildew. 

 The application of sulfur dust is effective on hops. 



REFERENCES 



Salmon, E. S. The strawberry mildew. Roy. Hort. Soc. (London) 

 Journ. 25 : 132-138. 1901. 



Berkeley, M. J. (No title) Gard. Chron. 1854 : 236. 1854. 



Anonymous. The strawberry mildew. Journ. Bd. Agr. 5 : 198201. 

 1898. 



Humphrey, J. E. The powdery mildew of the strawberry. Massa- 

 chusetts Agr. Exp. Sta. Rept. 1892 : 31-32. 1893. 



