FUNGI AFFECTING ALFALFA 



The Alfalfa Leaf-blight 



Cercospora helvola var. medicaginis 



This disease has been studied by Professor F. D. 

 Chester, of Delaware, who reports that it "shows itself 

 upon the leaf as sub-circular, or elliptical spots of a 

 smoky brown, or almost black color, equally visible upon 

 both sides, and vary- 

 ing from one-six- 

 teenth to one-thirty- 

 second of an inch in 

 diameter. The spots 

 are without well-de- 

 fined borders, which, 

 when closely exam- 

 ined, are somewhat 

 irregular, shading in- 

 distinctly into the 

 surrounding leaf tis- 

 sue. Spots coales- 

 cing cause the leaf to 

 turn yellow and brown, completely destroying it." 

 The same fungus is believed, occasionally, to attack 

 the red clover and scarlet clover, although it is seldom, 

 if ever, seriously destructive to these crops. The myce- 

 lium threads of the fungus push about between the cells 

 of the leaf, absorbing their contents, and causing the 

 discoloration of the foliage. When ready to fruit, the 

 threads develop abundantly at certain points just beneath 



'317 



FIG. 88. ALFALFA BLIGHT FUXGUS. 

 a, Spore; 6, section of leaf. Magnified. 



