324 



Diseases of Economic Plants 



is the only one to be recommended for alfalfa. It has been 

 very destructive in Texas since 1892. 



Anthracnose ^''•* {Colletotrichum trifolii Bain). — Alfalfa 

 anthracnose was first mentioned in 1905 l^y Bain and Essary, 



who stated that it was prev- 

 alent in Tennessee in 1906 

 and was one of the chief 

 causes of alfalfa failures in 

 that state. It has also been 

 noted in destructive form 

 in Virginia and New York. 

 It appears as elliptical, 

 sunken spots, 5-6 mm. 

 long, upon the stems. The 

 spots are gray and have 

 dark acervuli scattered 

 over them. Where the 

 disease l)ecomes aggressive, 

 dead or withered stalks or 

 plants are seen scattered 

 over the field. These stalks 

 arise from diseased crowns, 

 which are characterized by 

 blackening of the woody 

 parts, below the point 

 where the stalks are at- 

 tacked. The only remedy 

 seems to be the use of re- 

 sistant varieties. 



Blight ^"' ''^ (Pseudomo- 

 nas medicaginis Sack.). — 

 From Colorado Paddock, 

 in 1906, described a severe 

 disease of alfalfa which has 

 been noted for several successive years. It is due to bac- 

 teria and in its early stages produces a watery, semi- 

 transparent, yellowish to olive-green appearance along one 



Fig. 169. — Alfalfa crown-wart. 

 After U. S. Department of Agri- 

 culture. 



