STEMPHYLIUM LEAFSPOT OF CUCUMBERS^ 



By George A. Osner^ 



Associate Botanist, Purdue University Agricultural Experiment Station, and Collab- 

 orator, Cotton and Truck Disease Investigations, Bureau of Plant Industry, United 

 States Department of Agriculture 



INTRODUCTION 



In the latter part of September, 191 5, the writer discovered a pecuHar 

 leafspot on cucumbers (Cticumis sativus) in a small garden near Plymouth, 

 Indiana. The spots showed a distinctly mottled effect, and in some 

 cases were so numerous as to entirely kill the leaf. Specimens of this same 

 disease were discovered about the same time by Mr. W. W. Gilbert, 

 in two cucumber fields, one at Lapaz and the other at Lakeville, Ind., 

 and later, in a field at Bowling Green, Ohio. A field was found a few 

 miles from Plymouth in which over 40 per cent of the plants were afifected 

 by this disease. On many of these plants the leaves were so badly 

 affected as to considerably reduce the yield. During the summer of 

 1 91 6, no cucumbers were grown in any of the fields above mentioned and 

 although a sharp watch was maintained, the disease was not found in 

 the vicinity of Plymouth. However, while making a survey of the 

 cucumber fields in northern Indiana about the middle of September, 

 1 91 6, the disease was again found in fields around Hamlet, Lapaz, 

 and North Liberty. While the disease was not sufficiently wide- 

 spread to prove a serious economic factor in the growing of cucumbers, 

 observations indicate that in those spots of the field in which it occurred 

 the leaves were so badly injured as to reduce appreciably the yield for 

 pickles. 



SYMPTOMS OF THE DISEASE 



The disease first appears in the form of small yellowish spots on the 

 leaf, usually 0.5 to i mm. in diameter. The spots are soon visible 

 on both the upper and lower surfaces of the leaf (PI. 21, A, B). The 



1 These investigations were carried out at Plymouth and Lafayette, Ind., by the Office of Cotton and 

 Truck Disease Investigations, Bureau of Plant Industry, United States Department of Agriculture, and the 

 Purdue University Agricultural Experiment Station. 



^ The writer wishes to express his thanks to Prof. H. S. Jackson, of Purdue Experiment Station, and to 

 Mr. W. W. Gilbert, of the Bureau of Plant Industry, for helpful suggestions and criticisms during the 

 progress of this work. 



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



Washington, D. C. Apr. 29, 1918 



ne. (295) Key No. Ind.-j 



