100 U.S. DEPT. OF AGRICULTURE MISC. PUB. 939 



through bark wounds. Infected trees are killed by girdling or by stem 

 breakage at cankers. Losses are heavy, up to 70 percent mortality in 

 some stands. 



Intercontinental spread is possible through shipment of infected 

 trees or cuttings or of infected bark on logs or lumber. Importation 

 of living plant material other than pollen or seed should be forbidden 

 except for experimental use following rigorous inspection and reten- 

 tion in quarantine until all latent infections have had time to appear. 

 Export logs and lumber should be debarked. 



Range: In North America it is common from eastern Canada south 



to Virginia and west to the Great Plains; scattered in western 



United States and Canada. 

 Hosts: Salicaceae (species listed in order of susceptibility) — 



Populus tremuloidss Michx. 



P. grandidentata Michx. 



P. balsamifera L. 



P. tremula L. (planted in U.S.) 



P. adenopoda Maxim, (planted in U.S.) 



P. alba bolleana Lauche (planted in U.S.) 

 Literature : 



Bier, J. E. Studies in forest pathology. III. Hypoxylon canker 



poplar. Canad. Dept. Agr. Tech. Bui. 27 : 1-40. 1940. 

 Gruenhagen, R. H. Hypoxylon pruinatum and its pathogenesis 



on poplar. Phytopathology 35 : 72-89. 1945. 



Cedar Leaf Blight 



J..S. Boyce 



Professor Emeritus of Forest Pathology, Yale University, New 



Haven, Connecticut 



Keithia thujina Durand is a leaf disease of western red cedar in 

 North America. Worse in localities of high atmospheric humidity. 

 The lower branches of young trees, when growing in dense stands, 

 often appear at a distance as if scorched by fire. Foliage of the upper 

 crowns of mature trees may be generally infected but never to the 

 same degree as leaves on lower branches near the ground. In late 

 autumn the young infected leaf twigs drop, leaving the branches some- 

 what bare. On leaves remaining attached to the older twigs the fructi- 

 fications drop out leaving deep pits. The fructifications (apothecia) 

 are usually on the upper surface of the leaves, although they occa- 

 sionally occur on the undersurface They are embedded in the leaf 

 tissue and are exposed by the rupture of the epidermis in a flap- or 

 scale-like manner. The apothecia are cushionlike, depressed when 

 the air is dry, elevated when it is moist, and are circular, elliptical, 

 curved or irregular in outline. The apothecia are olive brown at first 

 but, with age, become almost black. Each ascus has two hyaline el- 

 liptical or pyriform spores, which when mature become olive brown 

 and nearly circular in shape. The spores are pitted and very un- 

 equally two-celled. The paraphyses are club-shaped and single or 

 branched. They have cross walls. No conidial stage is known. 



This is a severe foliage disease of western red cedar in North 

 America. Primarily a disease of seedlings and saplings, trees less 



