48 A PLANT-DISEASE SURVEY IN TEXAS. 



DISEASES OF FORAGE CROPS. 

 ALFALFA. 



Leaf -spot {Cercospora medicaginis Ell. and Ev.). — This disease on 

 the leaves of alfalfa {Medicago sativa L.) shows as dark-brown, cir- 

 cular or subcircular areas, 1 to 5 mm. in diameter. The spots on a 

 single leaflet may vary in number from one to nine and with a pre- 

 dominant size of 2 to 3 mm. "\Mien the spots are few in number each 

 is surrounded by an indefinite zone of yellow, and when abundant 

 the entire intervening areas become yellow. Many of the affected 

 leaflets fall from the plant, thus producing considerable defoliation. 



This disease was first reported from College Station, Tex., in 1891 

 (20), and has been reported more recently from New York (49). 



Specimens collected : San Marcos, 2103 ; Victoria. 2528 ; Gonzales, 2700. 



Leaf -spot {PseudopezizamedlGagims (Lib.) Sacc). — Observed only 

 in a single locality, at which place it was very abundant in an irri- 

 gated field. 



Specimen collected: San Marcos, 970. 



Root-rot {Ozoninm omnivcyfrnrb Shear). — This disease is caused by 

 the same fungus which produces the well-known root-rot of cotton. 

 It was observed only in a single field, where it caused a loss of 25 

 to 30 per cent. 



Specimen collected : Beeville, 1841. 



Eust {Uromyces medicaginis- falcatae (DC.) Wint.). — This disease 

 causes the formation of minute circular or elongated pustules of a 

 reddish-brown color. The epidci'mis is ruptured and the spore mass 

 is surrounded by the irregulai lacerated remains. Onh^ uredo pustules 

 have been observed in our specimens and these are more abundant on 

 the under surface than upon the upper surface of the leaflets (27). 

 Freeman does not mention the occurrence of the pustules upon the 

 upper surface of the leaflets. A single leaflet may show 20 to 60 

 pustules and still retain its green color in portions not occupied by the 

 pustules, while others having a lesser number of pustules may show 

 considerable yellowing. The disease does not cause serious damage 

 since only a slight degree of defoliation results. It is apparently the 

 least injurious of the three leaf diseases in this territory. 



Specimens collected: Collins's Garden. San Antonio, 1390: Brack ranch. 

 Cotnlla, 2204. 



COWPEA. 



Leaf -spot {Cercospora vlgnae Racib.^. — This is probably the most 

 common disease of the cowpea {Vigna unguicidata (L.) Walp.) in 

 this territory. It produces on the foliage large, circular, brown spots 



226 



