MAPLE DISEASES 225 



to the ground, the mycelium inside the black spots develops 

 ascospores. These are matiu-e in the spring. With the return 

 of warm weather, the black layer of fungous tissue cracks 

 open and the edges fold back, exposing the fruiting-layers 

 within. The spores are probably shot into the air as are most 

 ascospores. The young maple leaves are infected by the 

 ascospores which lodge upon them and germinate. 



Control. 



Very little trouble will be experienced from this disease if 

 the affected leaves are destroyed by burning in the autumn. 

 Unless this is carefully done and all the affected leaves under 

 and around the trees are destroyed, the few remaining ones 

 may cause some infection in the spring. In exceptional cases, 

 as in nurseries, spraying with bordeaux mixture as the leaves 

 develop may be desirable. For general directions on spraying, 

 see page 357. 



References 



Stewart, F. C. Black spot, Rhytisma acerinum (Pers.) Fr. In 



Notes on New York plant diseases, 1. New York Agr. Exp. 



Sta. (Geneva) Bui. 328 : 364. 1910. 

 Sohrenk, Hermann von, and Spaulding, P. Tar-spot. In Diseases of 



deciduous forest trees. U. S. Dept. Agr. Bur. PI. Ind. Bui. 



149 : 19. 1909. 



Black-Specked Leaf-Spot 



Caused by Rhytisma punctatum Fries 



The silver maple of eastern United States {Acer saccharinum) 

 and the broad-leaf maple (A. macrophyllvm) of the Pacific 

 Coast are occasionally affected by this leaf-spot. It does not 

 seem to be as abundant as the tar leaf-spot. During the 

 summer light green or yellowish areas about a half inch in 

 diameter appear in the leaf. Later several isolated black 

 spots the size of a pin-head develop on the upper surface of 

 the spot. In the autumn the affected area remains yellowish 



