May 6, 1918 Canker of Poplars and Willows 341 



On Populuf wislizeni: 



Flagstaff, Arizona, July, 1916 (FP 21262). 



Albuquerque, November, 1915 (FP 19919); by R. M. Harsch, September, 1916 

 (FP 21605); and Domingo, New Mexico, by R. M. Harsch, August, 1915. 



El Paso, August, 1915; and Pecos, Texas, November, 1916 (FP 21717). 

 On Salix amygaloides: 



Denver, Colorado, by E. Bethel, June, 19 13 (FP 8452). 

 On Salix bahylonica: 



Albuquerque, New Mexico, September and August, 1915 (FP 19493). 

 On Salix wrightii: 



Yuma, Arizona, December, 1915 (FP 21764). 



DISTRIBUTION IN MEXICO 



On Populus sp. (Alamo poplar), Juarez, 1912. 

 On Populus italica, Juarez, 1912. 

 On Populus wislizeni, Juarez, 1912. 



From the foregoing data it will be noted that 14 species of trees are 

 attacked by Cytospora chrysosperma, as follows: Populus acuminata, 

 P. alba, P. angustijolia, P. balsatnifera-suaveolens, P. deltoides, P. italica, 

 P. macdougali, P. sargentii, P. tremuloides, P. wislizeni, Populus sp. 

 (Alamo poplar), Salix amygdaloidcs, S. bahylonica, and S. wrightii. 



CONTROL OF THE DISEASE 



Certain species of poplars have been found to be more susceptible to 

 this disease than others. Therefore, only those species of poplars 

 which are most resistant to the disease should be selected for planting 

 in regions where this disease is common. The Carolina poplar and the 

 silver-leaf poplar are highly susceptible to this disease under the condi- 

 tions obtaining in a dry climate like that of the Southwest. When 

 these two species of trees are about 12 to 14 inches in diameter at the 

 ground, they usually show, in the crown, an increasing number of large, 

 dead branches which have been killed by Cytospora chrysosperma. 

 In fact, the writer has never examined a large tree of either of these two 

 species in Arizona or New Mexico that has not been seriously injured 

 or finally killed by the disease. This is particularly true in the vicinity 

 of Albuquerque, N. Mex. The Carolina poplar is also attacked in this 

 western country by two insect parasites which weaken the trees and 

 make them unsightly and more easily infected by this disease. One is 

 the cottony scale (Pulvinaria sp.), which usually seriously deforms the 

 trees, and the other insect is the poplar borer (Sapcrda sp.). This 

 species of poplar has, therefore, three serious enemies with which to con- 

 tend in this arid country and should not be planted as an ornamental 

 or shade tree. 



The native valley cottonwood (Populus wislizeni) is highly resistant 

 to the disease caused by Cytospora chrysosperma when given any kind 

 of care and attention and should be selected for planting in those por- 

 tions of the Southwest within its range. On account of the large amount 



