DANGEROUS INTERNATIONAL FOREST TREE DISEASES 65 



kova roku 1956. (Infections of different poplar clones by the rust 

 fungus Melampsora allii-populina Kleb. in the selection nursery of 

 Gabcikova in 1956) . Les. cas., IV, 1 : 30-45. 1958. 

 Vujic, P. Problem Melampsora i drugih obolenja lista i borba protiv 

 njih u plantazama topola (Problem of Melampsora and other leaf 

 diseases including measures against them in poplar plantations) . 

 Mimeopr. Savet. centar polj. i sum., Beograd, 20 pp. 1959. 



Bacterial Canker of Ash 



Pseudomon<as fraxini (Brown) Skoric (Syn. : Bacterium, savastanoi 

 Smith var. fraxini Brown) . This pathogen causes numerous perennial 

 stem and branch cankers of ash in Europe. Cankers are mostly of a 

 sunken and less frequently of a knobby type. Very young cankers 

 appear as one or two splits in the periderm and are followed by cross- 

 splits and openings of the bark. In the more advanced stage the 

 bark tissues become definitely broken down to the sapwood, imparting 

 a blackish or brownish color to it. At the same time, the bark border- 

 ing the canker begins to grow more vigorously, resulting in the forma- 

 tion of swellings and the enlargement of callous rings around cankers. 

 Small cankers of the sunken type are formed in 1 to 2 years and 

 large ones, reaching 10 to 20 cm. in diameter, in 10 to 30 years. 



Trees of all ages are susceptible. The disease is common in pure or 

 mixed ash stands, in parks, and along avenues. Valleys and localities 

 with a high relative humidity offer the best conditions for the develop- 

 ment of cankers. It is believed that the causal agent spreads mainly 

 by rain and probably by the common ash beetle (Leperisinus fraxini 

 L.) or even by mites. Wounds of any kind are the main entries 

 through which bacteria penetrate into cortical tissues. 



Deformations of the stem, stunted growth, and bushlike appearance 

 of attacked individuals are the principal kinds of damage. Esthetic 

 value of affected trees grown as ornamentals is reduced. Mortality 

 of young plants may result from rapid stem girdling. 



Possibility of spread. — Intercontinental spread is possible through 

 shipment of infected young plants and unbarked logs. The organism 

 may spread on unsterilized ash seeds originating in infected areas. 



Range: The disease has been reported chiefly in Austria, France, 



Great Britain, Italy, Netherlands, and Yugoslavia. 

 Hosts: English ash (Fraxinus excelsior L.) is reported as the most 



susceptible species. White ash (Fraxinus americana L.) and 



green ash (Fraxinus pennsylvanica lanceolata (Borkh.) Sarg.) 



are also found to be attacked. 

 Literature : 

 Brown, N. A. Canker of ash trees produced by a variety of the 



olive-tubercle organism, Bacterium savastanoi. Jour. Agr. Res. 



44:701. 1932. 

 Skoric, V. Jasenov rak i njegov uzrocnik (The ash-canker disease 



and its causal organism) . Glasnik za sumske pokuse, Zagreb, 6 : 



66-97. 1938. 



