328 Diseases of Economic Plants 



country. The affected parts of the leaf turn yellowish gray to 

 purple, and are frequently curled. The leaves, as seen from 

 below, are coated with a downy fuzz, violet colored when old. 



Rust (Uromyces striatus Schr.) may be recognized by the 

 typical rust sori, which are present, in this case, chiefly upon 

 the lower sides of the leaves. The cluster-cup stage is found 

 on Euphorbia. Anthracnose (Gloeosporium medicagitiis E. & 

 K.). — Black, rather prominent acervuli appear chiefly upon 

 the lower surfaces of leaf-spots. The lower leaves often 

 turn yellow and die. Seed-mold {AUernaria sp.). — Brown, 

 dead, shriveled seeds are often noted in samples of alfalfa 

 seed. Such seeds, if planted, develop, apparently from 

 within, a dense black mold. 



Damping-ofif (Rhizoctonia sp. and Pythium deharyanwn 

 Hesse) is caused chiefly by the two fungi named. It has 

 been known to affect alfalfa seedlings in the greenhouse, 

 and it may occur to some extent in the field, especially the 

 form caused ])y Rhizoctonia. 



Stagonospora leaf-spot (Stagonospora carpathica Baeu.) 

 has been noted only in New York. Stewart, French and 

 Wilson characterize this leaf-spot as follows: Unlike the 

 Ascochyta leaf-spot, this disease attacks chiefly green leaves 

 in the upper part of the plant. The spots are circular, 

 1-3 mm. in diameter, and usually light brown with a narrow 

 border of dark brown. Each spot bears several light brown 

 pycnidia visible on both surfaces of the leaf. Yellow-top 

 may appear simultaneously over whole fields. The cause is 

 unknown. White-spot is common but also is of unknown 

 cause. 



CLOVER 



Black-mold (Phyllachora trifolii (Pers.) Fcl., Polythrin- 

 cium). — Common red clover, crimson clover, white clover, 

 alsike clover, and several other related plants are affected by 

 this mold. The chief symptoms are pale spots upon the upper 

 sides of the leaves accompanied by Ijlack dots on the lower 

 sides. These spots at first glance so strongly resemble the 



