242 



MANUAL OF TREE DISEASES 



of many kinds of trees (Fig. 46). The second species Is a variety 

 of the first, seemingly confined to eastern, southern and central 

 United States, while the fom-th is so far reported only from 

 California. All of these fungi cause powdery white patches on 



Fig. 46. — Powdery mildew on oak leaf. 



both sides of leaves, but do little damage. The black or brown- 

 ish fruiting-bodies can be seen scattered or in clusters over the 

 affected area of the leaf. The life history and methods of con- 

 trol of powdery mildew fungi are discussed on page 37. 



