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



Literature : 



Anonymous. Control of Dutch elm disease and elm phloem necrosis. 

 U.S. Dept. Agr. Leaflet 329: 1-11. 1952 



Baker, W. L. Transmission by leaf hoppers of the virus causing 

 phloem nercosis of American elm. Science 108 : 307-308. 1948. 



Swingle, Roger U. Phloem necrosis. A virus disease of the Ameri- 

 can elm. U.S. Dept. Agr. Cir. 640 : 1-8. 1942. 



Atropellis Canker of Pine 



J. C. Hopkins 



Forest Entomology and Pathology Branch, Canada 

 Department of Forestry, Calgary, Alberta 



Atropellis piniphila (Weir) Lohman and Cash. A perennial canker 

 on stems and branches of pines. The processes of disease develop- 

 ment involving this pathogen have been examined in detail only on 

 Pinus contorta in Alberta. The first symptom, consisting of a drop 

 of resin on the surface of the bark, is frequently followed soon after- 

 wards by rupture of the bark, revealing an underlying resin pocket. 

 Fresh resin flow occurs early each summer from the canker margin 

 throughout growth of most cankers. 



The fungus invades all stem tissues, but grows more rapidly within 

 the outer sapwood than within the bark. Growth is fairly slow in 

 all directions, but proceeds much more rapidly in a longitudinal di- 

 rection than in any other, resulting in a more or less diamond-shaped 

 canker. Invasion inward within the wood proceeds primarily along 

 the rays, but later spread laterally into the tracheids. The invaded 

 wood is characterized by a blue-black discoloration, and frequently 

 develops a peripheral incipient zone which possesses a reddish-brown 

 color. Apothecia are formed on the surface of the bark at the canker 

 centers, and formation continues at a distance of 6 to 9 inches from 

 the longitudinal apices of the cankers. 



The apothecia are erumpent, brownish to black, and 2 to 5 mm. in 

 diameter when expanded by moistening. The clavate asci, inter- 

 spersed with paraphyses, each contain eight hyaline, elliptical- 

 fusoid ascospores, 16-22 X 4-5/u,, which may be 1- or 2-celled before 

 germination. 



The disease is spread by ascospores, probably wind disseminated, 

 which are released during wet weather in the growing season. Infec- 

 tion of the stems occurs mainly at the branch nodes. Girdling of the 

 stem is very slow, but mortality may be produced in hitherto vigorous 

 trees as a result of the occurrence of two or more cankers at the same 

 level. Multiple stem cankers, common in high incidence areas, may 

 cause considerable degrading of the wood for use as pulp or lumber. 



Intercontinental spread possible, either through shipment of in- 

 fected trees or infected bark on logs. Export logs should be debarked. 



Range : This pathogen appears to form high incidence zones, mainly 

 on Pinus contorta in Alberta and British Columbia. On this and 

 other hosts, it occurs on a number of locations in western North 

 America, including Montana, Idaho, Washington, Oregon, Ari- 

 zona, and New Mexico ; it has also been reported from Alabama 

 and Tennessee. 



