338 Diseases of Economic Plants 



VETCH 



Spot {Protocoronos'pora nigricans A. & E.). — Upon the 

 stems, leaves, and bracts of vetch very characteristic, long, 

 narrow, or elliptical spots are formed, frequently with a dull 

 purple border, and usually with a white center. When on 

 the pods, they are obliquely situated. When old, they ap- 

 pear as black, oblique lines. No serious damage has been 

 reported. 



Downy-mildew {Peronospora vicioe (Berk.) De Bary); 

 Powdery-mildew {Erysiphe); Rust {Uromyces sps.), and 

 Leaf-spot {Mycosphcerella) see pea, are of minor importance. 



Grasses 



Many of the diseases listed below on special grasses should 

 perhaps be considered as general grass diseases. Thus the 

 smut, Ustilago striceformis, is known on many genera of 

 grasses. Grasses in general are susceptible to powdery- 

 mildew, Phyllachora, Ergot, and rust. The biologic rela- 

 tionships of but few of these have as yet been studied on 

 account of their comparatively small economic significance. 



BARNYARD -GRASS (Panicuni) 



Smut (Ustilago crusgalli T. & E.) is common and is i-eadily 

 recognized by the usual smut characters. No treatment is 

 recommended. 



BLUEGRASS (Poa) 



Rust (Puccinia poaruni Niels.). — The uredinia of this 

 rust take even greater prominence than do the uredinia of 

 other rusts; indeed other forms of spores are almost entirely 

 absent in most parts of the country, throwing the burden of 

 perpetuation of the species entirely upon the uredinial 

 mycelium and its spores. This stage is known to be peren- 

 nial as far north as Washington, D. C., Nebraska, and Min- 

 nesota. The secia occur on Tussilago. 



