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, Spherotheca 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. Asa 
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. 26: 132-138. 1901. 
Berkeley, M. J. (No title) Gard. Chron. 1854: 236. 1854. 
Anonymous. The strawberry mildew. Journ. Bd. Agr. 5: 198-201. 
1898. 
Humphrey, J. E. The powdery mildew of the strawberry. Massa- © 
chusetts Agr. Exp. Sta. Rept. 1892: 31-32. 1893. 
