382 DISEASES OF ECONOMIC PLANTS 



spot has been noted in North CaroUna, 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. The disease is not important. 



Cercosporose {Cercospora Medicaginis Ell. & Ev.). — This 

 disease appeared in Delaware in 1889 and has also been 

 noted in New York and New Jersey. 



The leaf spots are nearly circular, 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 bor- 

 ders, but shade into the surrounding healthy tissue. Af- 

 fected leaves turn yellow and die. 



Pseudomonose {Pseudomonas Medicaginis Sackett). — 

 From Colorado Paddock,' in 1906, described a severe dis- 

 ease of alfalfa which has been noted for several successive 

 years. 



It is due to bacteria ' and in its early stages produces a 

 watery, semitransparent, yellowish to oUve-green appear- 

 ance along one side of the stem of the plant. The plants 

 are at first weak, and light colored, then discolored or black- 

 ened on the stems. Drops of thick fluid ooze from the 

 stems and dry upon them, giving a glistening appearance as 

 if they were varnished. The chief damage is to the first 

 cutting, though in subsequent years the plants may die 

 from decay of the crown, or roots, or from loss of nutrition. 

 Infection seems to be chiefly through rifts in the epider- 

 mis due to frost, and is caused by wind-borne bacteria. 



' Paddock, W., Col. Agr. Exp. Sta. Press Bui. 28, November, 1906. 

 ^ Sackett, W. G., Soc. Am. Bact., Boston meeting, December, 1909. 

 Also Colo. Agr. Exp. Sta. B. 158, 1910. 



