Strawberry Powdery Mildew was first reported from England in 1854, at which time it was of considerable importance. In 1885 it again became noticeable in England. The next year it was found in America (New York State). In 1892 it was recorded from Massachusetts, but prior to 1896 the disease was rarely serious in the United States. Now the disease is common and widespread and is capable of doing serious damage.

Sometimes all varieties are affected; again certain ones are immune. Among the susceptible varieties may be noted: Paxton, British Queen, Black Prince, Jucunda, Mount Vernon, May King and Garrettson. On the other hand, the Noble and Royal Sovereign are said to be resistant.

Symptoms

In the first stages the leaves are affected. They curl at the margin and thus expose their lower surfaces. Affected plants present an appearance as in need of water. Powdery, white growth of the mildew-pathogene appears on the lower surface. This is frosty and mealy in aspect. Berries are affected in all stages of development. They are rendered tasteless and 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 cannot 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: 198 - 201. 1898.

Humphrey, J. E. The powdery mildew of the strawberry. Massachusetts Agr. Exp. Sta. Rept. 1892: 31 - 32. 1893.