JOIMAl OF AGKIOllTlAl RESEARCH 



Vol. XIII Washington, D. C, May 6, 1918 No. 6 



YELLOW-LEAFBLOTCH OF ALFALFA CAUSED BY THE 

 FUNGUS PYRENOPEZIZA MEDICAGINIS^ 



By Fred REuEt Jones 



Pathologist, Cotton, Truck, and Forage Crop Disease Investigations, Bureau of Plant 

 Industry, United States Department of Agriculture 



INTRODUCTION 



In the spring of 191 4, when the writer began a study of the foliage dis- 

 eases of alfalfa {Medicago saliva) in the vicinity of Madison, Wisconsin, 

 special attention was given to the leafspot caused by the fungus Pseudo- 

 peziza medicaginis, which is generally regarded as the most important 

 disease of this plant. But it soon became apparent that another dis- 

 ease, which had not previously been mentioned as occurring in the 

 United States, was responsible, under certain conditions at least, for 

 even greater damage to the crop than the well-known leafspot. A study 

 of this disease was undertaken in addition to the work on leafspot, and 

 a brief report was made in 191 6 (10).^ Since that time the work on 

 this disease has been continued, stimulated by an increasing recognition 

 of its importance. The results are presented in the following pages. 



THE DISEASE 



DISTRIBUTION 



During the two summers which have elapsed since the yellow-leaf- 

 blotch was first noted in the United States, there has not been oppor- 

 tunity to make a complete survey of its distribution. It has been col- 

 lected by the writer or correspondents in Vermont, New Jersey, Virginia, 



' This paper presents one part of the results of a study of a group of alfalfa and clover diseases, which 

 was begun in the Department of Plant Pathology at the University of Wisconsin in 1914. In 1916 the 

 writer became a collaborator of the Office of Cotton, Truck, and Forage Crop Disease Investigations, of the 

 Bureau of Plant Industry, and through cooperation between the Bureau and the Wisconsin Agricultural 

 Experiment Station, the scope of the work was extended. The work has been done under the immediate 

 direction of Dr. L. R. Jones, to whom grateful acknowledgments are expressed. Other members of the 

 Department of Plant Pathology at the University of Wisconsin have contributed many valuable sug- 

 gestions, and several correspondents have furnished specimens and information which have added greatly 

 to the value of the work. 



- Reference is made by number (italic) to " Literature cited," p. 3:9. 



Journal of Agricultural Research, Vol. XIII, No. 6 



Washington, D. C. May 6, 1918 



nf Key No. G-142 



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