4M 



THE BLACK-SPOT DISEASE. 



times extensively attacked by this parasite, but in America it 

 has not been noticed to any great extent on the more valuable 

 Bpeeies— its presence being possibly overlooked in meadows be- 

 cause concealed by the spreading blades above. 



A black fungus related to this which occurs on grass, is Hy- 

 pocrella hypoxylon (Pk.). 



7. Black-spot disease of grass, {Phyllachora graminis, P.) 

 Coal-black spots usually under 1-33 in. wide, and 1-33-i in. long, 

 on the leaves of grasses; especially conspicuous on the upper side. 



This is one of the commonest and most no- 

 ticeable of grass-diseases, especially toward 

 the end of the season, but does little harm to 

 valuable species. It is most abundant on 

 quack grass, hedgehog grass and the broad- 

 leaved Panicum. The black spots are com- 

 posed of dense mycelium. In them, usually 

 after the death of the leaf, oval colorless spores 

 are formed in asei. These spores carry the 

 species over the winter. Smaller spores (stylospores) are pro- 

 duced in the same spots earlier, and servo for summer propaga- 

 tion. If the disease should prove troublesome, the grass may be 

 cut early before the fungus develops, and the meadow should be 

 burned over on the approach of cold weather to destroy the form- 

 ing winter spores. (Fig. 108 illustrates the above species.) 



8. Black-spot disease of clover, {Phtjlladiora trifolU, P.). 

 On the lower side of clover leaves, forming at first dull-black 

 patches, often ^-in. across; later occurring in the form of slightly 

 glossy-black dots, 1-64 in. in diameter, on small whitish or pale- 

 brown spots. 



¥\Q. leS—Phiillachora graminin. Fig. 169.— Phyllachora trifoUi. FiQ. 171.— Poly- 

 thrincium trifolU. Fia.—ilO.—Phacidiurn trlfoiii. 



