192 



THE FORAGE AND FIBER CROPS IN AMERICA 



fa is the leaf-spot (Pseudopezisa medicaginis (Lib.) Sacc.) 

 It is much more injurious in moist than in dry climates. The 

 evidences of it are usually first seen in the turning yellow of 

 the lower leaves. If these leaves are closely examined, they 



will be seen to contain numerous 

 small brownish-yellow blotches 

 in the center of which is a still 

 smaller black circle of fruiting 

 cups, each containing eight egg- 

 shaped or oblong ascospores. 

 The plant becomes infested by 

 these ascospores floating in the 

 air, particularly if the air is 

 moist. The disease spreads with 

 great rapidity, hence the desir- 

 ability of mowing the crop as 

 soon as attack begins to man- 

 ifest itself. (225) Experiments 



Alfalfa leaf attacked by leaf-spot . . r . 



Natural size with fungicides and with fer- 



tilizers at the Cornell Station 



gave negative results. Root-rot (Ozonium Sp.), a fungous 

 disease affecting cotton and other plants, also sometimes affects 

 alfalfa when it is grown in regions where cotton occurs. 



219. Insects. Few insects attacking alfalfa exclusively or 

 even chiefly have been reported. The principal insect enemy 

 of alfalfa in the western states is the ever-present grass- 

 hopper. The remedy against grasshoppers in general is said 

 to be deep plowing in the fall to bury the eggs and spring 

 harrowing to destroy them. When the alfalfa field is attacked 

 the Nevada Station recommends the use of the following 

 mixture just after the first crop is harvested: Paris green i, 

 common salt 2, fresh horse dung 60 pounds. This mixture is 

 to be scattered over the field when the hoppers are thickest, 

 in the morning while the soil is still wet from the first irriga- 



