392 Diseases of Economic Plants 



from the center outward in radial lines through the medullary 

 rays; the hard flinty wood is reduced to a soft, yellow, cheesy 

 mass, spongy when wet. The pore-bearing, shelving, hoof- 

 shaped, sporophores develop chiefly from the burrows of 

 the locust borers or from stubs. The young portions are 

 light brown; older parts, dark to black and fissured. The 

 lower side is dull red-brown. 



The rot ceases with the death of the tree, and posts made 

 from diseased wood do not continue to rot. 



MAPLE 



Leaf-spot (Phijllosticta acericola C. & E.). — A large propor- 

 tion of the leaf may become involved, causing premature 

 defoliation which materially lessens the value of the tree for 

 ornament or shade. The silver maples are especially sus- 

 ceptible, and their sale has thereby been reduced. The leaf 

 spot was first noted in 1874 and is distributed throughout the 

 United States. The blackish, subcircular spots as they en- 

 large change to brown and later to dirty white in the center 

 with black borders. Small black pycnidia may be seen in the 

 central regions of the mature spots, which are from 10-14 mm. 

 in diameter. Burning diseased leaves is recommended, ac- 

 companied by use of Bordeaux mixture if economy justifies. 



Tar-spot (Rhytisma acerinum Fr.). — Thick, shining, 

 irregular black spots 1-1.5 cm. across appear on the leaves in 

 late summer and cause them to fall prematurely, thus weak- 

 ening the tree. Considerable damage is often done to nur- 

 sery stock. The leaves should be raked together and burned 

 in the fall. 



Leaf-spot {Rhytisma punctatum Fr.). — In this leaf-spot 

 the causal fungus forms several small, black dots upon the 

 leaves as contrasted with the one large black blotch of the 

 tar-spot. 



Anthracnose {Gloeosporium apocryptum E. & E.). — Nur- 

 sery maples have been seriously injured by this anthracnose. 

 The tips of leaves of pruned twigs turn yellow, then blacken 



