HEART-ROT OF OAKS AND POPLARS CAUSED BY 

 POLYPORUS DRYOPHILUS 



By George G. Hedgcock, Pathologist, and W. H. Long, Forest Pathologist, Investi- 

 gations in Forest Pathology, Bureau of Plant Industry 



INTRODUCTION 



The oaks {Qtiercus spp.) of the United States are diseased by a number 

 of species of fungi which attack the heartwood. Von Schrenk and Spauld- 

 ing (1909)' briefly described some of these diseases and also a piped rot 

 of the heartwood of oaks and chestnuts {Castanea dentata) the cause of 

 which was unknown to them. In 1 909, the senior writer found Polyporus 

 dryophihis constantly associated with a whitish piped rot of several spe- 

 cies of oaks in the southwestern and western United States. This rot was 

 much like that described by Von Schrenk and Spaulding and was identical 

 with that of specimens in oak collected by them. Later observations by 

 the senior writer established the causal relation of Polyporus dryophilus 

 to this piped rot. 



The junior writer in 1913 found a second form of piped rot caused by 

 Polyporus pilotae in the heart-wood of the root and basal portion of the 

 trunks of oaks and also in chestnuts. This was identical with the rot in 

 chestnut trees figured and collected by Von Schrenk and Spaulding. 



The oaks of the southwestern and western United States are not used 

 to any extent for lumber and timbers and are, as a rule, valuable only for 

 fuel. This is due to the rotted condition of the heartwood in the larger 

 and older trees. For example, the trunks of the valley oak {Quercus 

 lobata),- which attains a large size in the valleys of central California, are 

 usually either badly decayed or hollow and are of no value except for the 

 poor grade of fuel they furnish. The senior writer in 1909 ascertained 

 that Polyporus dryophilus was the chief cause of the deterioration of the 

 oaks of the western United States. Meinecke (191 4) reports a destruc- 

 tive heart-rot of oaks caused by this fungus in California and Nevada, 

 and data by him will be cited in the section on the distribution of the 

 fungus. In Arizona and New Mexico the oaks are diseased in the heart- 

 wood nearly as badly as in California and Oregon, and P. dryophilus is the 

 common cause of decay. In these States oaks are usually small and are 

 valuable only for fuel. 



In Texas and the adjacent States of Oklahoma and Arkansas the 

 piped rot produced by this fungus is very common, and among other 



' Bibliographic citations in parentheses refer to " Literature cited, " p. 77. 



2 The nomenclature for trees used in this paper is that of George B. Sud worth ( 1898). 



Journal of Acricultural Research. Vol. Ill, No. i 



Dept. of A;:.'iculture, Washington. D. C Oct. 15, 1914 



G-34 

 (65) 



