MAPLE DISEASES 



227 



In wet seasons defoliation may result. The illustrations show 

 the effect of these diseases on the leaf (Figs. 37 and 38). Many 

 of the other leaf-spots of maple appear similar to these, however, 

 and no accurate 

 determination can 

 be made without 

 a microscopic ex- 

 amination of the 

 fungus. 



The leaf-spot 

 caused by Phyllo- 

 sticta minima is 

 characterized by 

 light brown cir- 

 cular spots with 

 numerous black 

 dot-like fruiting- 

 bodies near the 

 center (Fig. 37). 

 The general char- 

 acters of leaf- 

 spots, and the life history of the fungi causing them, are more 

 fully discussed on page 27. 



Fig. 38. — Leaf-spot of maple caused by Gloeosporium 

 apocryptum. 



Powdery Mildews 



Caused by Uncinula drdnata Cooke and Peck and Phyllactinia 

 corylea (Pers.) Karst. 



Two species of the powdery mildew fungi are known on 

 maple leaves in the United States, Uncinula drdnata and 

 Phyllactinia corylea (see page 35). The former has been 

 reported from northeastern and central United States and 

 the latter, which occurs on all kinds of trees, is distributed 

 throughout the country. These two diseases cannot be dis- 



