AN UNDESCRIBED CANKER OF POPLARS AND WIL- 

 LOWS CAUSED BY CYTOSPORA CHRYSOSPERMA 



By W. H. Long 



Forest Pathologist, Investigations in Forest Pathology, Bureau of Plant Industry, United 

 States Department of Agriculture 



INTRODUCTION 



In the semiarid regions of the Southwest tree growth is not favored by 

 climatic conditions as it is in the East. This is especially true of orna- 

 mental and shade trees suitable for homes, streets, and parks. Several 

 species of poplar (Populus spp.) and willow {Salix spp.) are able to grow 

 into beautiful ornamental and shade trees under the adverse conditions 

 in many of the Western States. Since there are so few species of shade 

 trees capable of growing in semiarid regions, it is of great importance that 

 special attention be given to any disease which may attack these trees. 



From time to time specimens of diseased bark from various species of 

 poplar have been received by the writer from several Western States, 

 accompanied by statements that the trees were being killed and requests 

 for information as to the cause of the trouble. On account of the serious- 

 ness and wide distribution of the disease, investigations as to its cause 

 and control were undertaken. This article gives the results of these 

 investigations. 



The disease has been found at various altitudes, ranging from i,ooo 

 to 8,000 feet. It is common in the semiarid regions of the Southwest on 

 various species of poplar, especially when used as shade or-ornamental 

 trees, and occasionally on willows. 



DESCRIPTION OF THE DISEASE 



This disease occurs in the form of lesions or cankers on the trunks and 

 large limbs of affected trees. It is also found attacking the small branches 

 and twigs. These are usually killed without forming any definite 

 canker. 



The lesions caused by this disease resemble what is often called "sun- 

 scald" on the trunks of fruit trees. The diseased bark is gradually 

 killed in more or less circular areas. Young infections on smooth-barked 

 shoots'can be recognized by the presence of brownish, shrunken patches. 

 However, these differ but little in general appearance from the surround- 

 ing healthy bark. 



The area invaded by the fungus may be fairly regular or very irregular 

 in outline. The diseased area gradually enlarges until the trunk or 



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



Washington, D. C. May 6, 1918 



nh Key No. G-143 



