CHAPTER XXVIII 

 POPLAR DISEASES 



A VAEIETY of common names is used to designate the dozen 

 or so species of Populus native in the United States. The dis- 

 eases of these trees are common to the different species and the 

 name poplar is used to designate the group except when certain 

 species are indicated. Poplars are important forest-species. 

 The common cottonwood is frequently used for shade and 

 ornament in regions in which trees are not abundant, because of 

 deficient rainfall. This tree is especially adapted to dry soils 

 and formerly, was used extensively as a street tree, until it 

 was found to damage sewers and drainage pipes by clogging 

 them with its roots. The European white and black or Lom- 

 bardy poplar are planted frequently as ornamentals. 



Poplars are subject to several types of diseases. The leaf- 

 rusts are destructive to young trees and seriously interfere 

 with their growth in the plains region. The newly introduced 

 European fungus which causes the poplar canker has already 

 proved to be a menace to young trees in the nursery. It is 

 also destructive on trees which are recently transplanted. 

 The importance of this disease cannot at present be prophesied, 

 since apparently it has not been in this country for any length 

 of time. In the forest the common white wood-rot is the most 

 destructive disease of poplars. 



Leaf-Rtjsts 



Caused by Melampsora Meditsoe Thum., M. ahietis-canadensis (Pari.) 

 Ludwig and M. albertensis Arthur 



Three leaf-rusts of poplars are common in the United States. 

 Two of these occur practically throughout the country, while 



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