Forage Crops 327 



tive in Arizona. It is a soil disease, and its general characters 

 are those indicated on p. 26. 



Root-rot {Rhizoctonia crocoriim DC). — Similar to the 

 effects of Rhizoctonia upon so many other hosts, the disease 

 consists primarily of a root-rot in which the diseased parts 

 are coated with matted strands of the fungous mycelium, 

 usually brownish red or violet in color, accompanied by 

 sclerotia. The tops of plants so diseased turn yellow and die. 



The very aggressive fungus migrates through or over the 

 soil to adjoining plants, and the affected spot in the field 

 thus enlarges, sometimes at a rate of 7 m. radially per year. 

 Though long known in Europe, it has not yet appeared in 

 many parts of America. 



Rhizoctonia root-rot is a typical soil disease and is kept 

 alive in the soil by its sclerotia, which may live at least two or 

 three years. The general suggestions given under soil dis- 

 eases apply. 



Ascochyta leaf-spot (Ascochyta medicaginis Bres.). — This 

 leaf-spot has been noted in North Carolina, and what is 

 probably the same disease, also in New York. The spots are 

 irregularly circular except where they occur on the edge of 

 the leaf, light brown in color, and bear small black dots. 



Cercospora leaf-spot (Cercospora jnedicaginis E. & E.), 

 which appeared in Delaware in 1889, has also been noted in 

 New York and New Jersey. The leaf-spots are nearly circu- 

 lai', smoky brown to black, from 0.5-1 mm. in diameter, and 

 show equally well from either surface of the leaf. They have 

 no well-defined borders, but shade into the surrounding 

 healthy tissue. Affected leaves turn yellow and die. It ap- 

 pears to be disseminated on the seed. Seed disinfection is 

 therefore recommended. A leaf-spot has also been described 

 due to Pleosphcerulina hriosiana Poll., and others due to 

 Septoria and Macrosporium. 



Downy-mildew (Peronosporn frifoUorum De Bary) is a 

 serious pest on clover in Ein'ope and has been reported in 

 America from Colorado, Kansas, New York, and North 

 Carolina, though it has not yet been destructive in this 



