DISEASES OP TRUCK CROPS. 37 



Chlorosis. — In one truck garden Kentucky Wonder beans were found 

 suffering from chlorosis to a marked extent. Tlie planti^ were de- 

 cidedly clilorotic and had made only a stunted growth. The roots 

 were sound, and neither fungous nor bacterial lesions could be found 

 on the aerial portions. A general examination of the field showed, 

 liowever, that the hypocotyls extended 4 to 6 inches beloAv the surface 

 of the ground. This abnormal length was due to deep planting with 

 subsequent ridging of the roAvs to provide irrigation furrows be- 

 tween rows. It seems probable that this abnormal depth of the 

 roots, combined with excessive irrigation was the cause of this 

 trouble. 



Specimen observed : Uvalde, 1965. 



Leaf-spot {Cercospora canescens Ell. and Martin). — A leaf-spot 

 disease of the Lima bean caused by the above fungus was observed in 

 a single locality. The spots are subcircular or angular, 1 to 5 mm., 

 with a gray center surrounded by a narrow, definite, reddish-brown 

 border, slightly less pronounced upon the under surface. The spots 

 are isolated, either few or abundant, and do not cause chlorosis to 

 any extent. (PI. IX, fig. 3.) 



Conidiophores are equally abundant on both surfaces, densely cespi- 

 tose (PI. II, fig. 5) J brown below, becoming hyaline tipped, several 

 septate, irregular, nodose in distal portion, 60 to 105 by 3 to 4.5 fi; 

 spores hyaline, slender club shaped, straight or curved, one to many 

 septate, 100 to 210 by 3 to 4.5 fi, or sometimes as short as 30 ^u, and 

 rarely equaling 6 /x in diameter. (PI. II, fig. 6.) 



Six different species of Cercospora have been described as affecting 

 the various species of Phaseolus. The sizes of the spores of these 

 species are as follows : Cercospora jjMseolina Speg., 20 to 45 by 3 to 

 3.5 fx\ C. phaseolorum Cke., 40 to 50 by 4 /x; C. colmnnaris Ell. and 

 Ev.j 40 to 60 by 5 /*; C. cruenta Sacc, 60 to 80 by 4 |m; C. canescens 

 Ell. and Martin, 100 to 120 by 5 to 6 /*; ^. oUvascem Sacc., 130 to 150 

 by 4 to 4.5 jn. 



It may be noted that our specimens show a size of spore different 

 from that recorded for C. canescens Ell. and Martin, but an examina- 

 tion of the specimens in the herbarium of the New York Botanical 

 Garden shows that they should be referred to this species. 



Specimen collected : Georgetown, 2365. 



Powdery mildew {Erysiphe polygoni DC). — This fungus forms a 

 dense white coating on the leaves causing them to become yellow and 

 dry. A crop grown in September was a total loss, and the June crop 

 was seriously affected in the one locality where it was observed. 



Specimen collected: San Antonio, 3149. 

 226 



