356 FOE AGE PLANTS AND THEIR CULTURE 



wise, there is likelihood of the alfalfa becoming infested 

 by the dodder seed in the soil. 



420. Diseases. Alfalfa is subject to various fungous 

 diseases, but it is exceptional for any of these to cause 

 large damage, though the aggregate loss is considerable. 



Root-rot (Ozonium omnivorum) occurs in Texas and 

 Arizona, and attacks many other plants besides alfalfa. 

 It appears on the roots as orange-colored threads. The 

 attacked plant nearly always dies. The fungus gradually 

 spreads to surrounding plants, which, with 'the rotting of 

 the root, wilt and then die. Rarely a plant may survive 

 by sending out new roots from near the crown. The circles 

 of dead plants caused by this disease are characteristic. 



Only indirect means of treatment can be used. The 

 root-rot fungus thrives best in poorly ventilated soils, 

 and further is not known to attack any monocotyledonous 

 plant. The growing of such crops as corn, sorghum, the 

 small grains and grasses, in rotation tends to free the land 

 from the fungus. 



At the Ohio Experiment Station a root-rot caused by 

 Fusarium roseum has been found killing young alfalfa 

 seedlings. 



Bacillus tumefaciens, the organism of crown-gall on 

 fruit trees, sometimes affects alfalfa, causing small irregu- 

 lar nodules on the roots and stems. Affected plants have 

 been found in Kentucky, Maryland, Pennsylvania and 

 Alabama. The affected plants are stunted somewhat, 

 but no serious damage to fields has yet been traced to this 

 organism. 



Urophlyctis alfalfa is a fungus that causes wart-like 

 excrescences to appear near the crown, both on the larger 

 roots and on the bases of the stems. The galls are usually 

 small, but may become 3 or 4 inches in diameter. This 



