CHERRY DISEASES 177 
Powvery-MILDEW 
Caused by Podosphera Oxyacanthe (Fries) de Bary 
It is chiefly the young leaves and the tips of branches of 
young cherries that suffer from the effects of powdery-mildew. 
But the disease is commonly observed also on mature trees. 
Furthermore the mildew pathogene attacks other fruit-trees 
like the apple, plum, peach, crab-apple, quince and persimmon, 
as well as certain shrubs, including juneberry, hawthorn, 
spirea and huckleberry. 
Cherry powdery-mildew was first described in France about 
1800, on hawthorn. Subsequently it was discovered in Germany 
on the cherry. In America the disease is very common and 
widespread in the eastern and central states, and is reported 
from the Rocky Mountain states and California. It also occurs 
in Canada. 
The pathogene shows preference for budded sour cherry 
stock, although sweet varieties and mazzards are known to 
suffer from its attacks. The mahaleb cherry and the variety 
Governor Wood, a sweet variety, have exhibited a certain 
amount of resistance, while the Hoy variety has been noted as 
free from mildew in cases where other varieties succumb. 
Symptoms. 
Powdery-mildew is usually found on the young sprouts and 
at the tips of branches, where it affects both the foliage and the 
wood (Fig. 49). It may be observed as early as the first of 
June, but does not develop sufficiently to attract attention 
until July, and it increases in prominence throughout the late 
summer and early autumn. Affected parts show small, round, 
whitish blotches, having a radiating appearance. These blotches 
spread and coalesce so that a considerable portion of an affected 
leaf or twig becomes covered by a white felt. These mildewed 
spots soon exhibit black spherical bodies which are scattered 
N 
