CHERRY DISEASES 177 



POWDERY-MILDEW 

 Caused by Podosphcera Oxyacanthce (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, 

 spirsea 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 



