ANGULAR-LEAFSPOT OF CUCUMBER: DISSEMINATION, 

 OVERWINTERING, AND CONTROL 



COOPERATIVE INVESTIGATIONS BETWEEN THE UNIVERSITY OP WISCONSIN AND 

 THE BUREAU OF PLANT INDUSTRY, UNITED STATES DEPARTMENT OF AGRI- 

 CULTURE 



By EuBANKS Carsner' 



Fortnerly Heinz Fellow in Plant Pathology, University of Wisconsin, and Collaborator, 

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

 Industry, United States Department of Agriculture 



INTRODUCTION 



The bacterial nature and the S5Amptoms of the angular-leafspot of 

 cucumber (Cucumis sativus) have been clearly described by Smith and 

 Bryan {15).'^ Prior to this paper the disease had been reported in this 

 country by Burger {1-4) and from Europe by Traverso {16) and Poteb- 

 nia {12). The two latter writers accepted Burger's statement that the 

 organism which caused the spots on the leaves was also responsible for 

 a serious rotting of the fruit. The inoculation studies made by Smith 

 and Bryan {15) showed that the bacterium which caused the leaf-spotting 

 was unable to produce a soft-rotting of the fruit. Extensive tests by 

 the writer have confirmed their finding in this regard. 



The bacterial cause of the disease was determined independently by 

 the writer in the summer of 191 5, as set forth in a preliminary note (5). 

 The morphological and physiological studies which were subsequently 

 made of a strain of the causal organism isolated from a Wisconsin speci- 

 men gave results essentially in agreement with those reported by Smith 

 and Bryan (75). The name given to the organism by these writers is 

 "Bacterium lachrymans." According to Migula's system of classification 

 it would be called "Pseudomonas lachrymans." 



The damage caused by the angular-leafspot can not be accurately 

 estimated. It varies greatly with differing weather conditions, but enough 

 weather favorable for the disease prevails each year to make the injury 

 of considerable importance (PI. 13, A). The writer's ideas as to the 

 destructiveness are based mainly on his field experience in Wisconsin 

 and adjoining States during three summers, together with more limited 

 observations in Virginia and southern California. 



It is when the disease appears in a field early in the summer that the 

 greatest damage results, as would naturally be expected. Young plants 



1 The writer wishes to express his appreciation to Dr. L. R. Jones, of the Wisconsin Experiment Sta- 

 tion, for helpful interest and advice in the prosecution of the work and to thank Mr. W. W. Gilbert and 

 Dr. M. W. Gardner, of the Bureau of Plant Industry, for helpful suggestions and cooperation. 



* Reference is made by number (italic) to " Literature cited," p. 220. 



Journal of Agricultural Research, Vol. XV, No. 3 



Washington, D. C. (201) Oct. 21, 1918 



pw Key No. G-160 



