DANGEROUS FOREST DISEASES IN 

 YUGOSLAVIA 



M. M. Krstic 





Professor, Forestry Faculty, University of Belgrade, Belgrade, 



Yugoslavia 



Leaf and Twig Blight of Poplars 



Venturis populina (Vuill.) Fabr. (Imperfect stage: Pollaccia ele- 

 gans Serv.) . This disease attacks young leaves and snoots of different 

 poplars, causing blackening and withering of these organs in the 

 spring (usually May in southern Europe) . The common Italian name 

 for the disease is "Defogliazione primaverile" (Spring defoliation). 



The fungus. — Brown hyphae on the infected organs bear brown- 

 ish, mainly two-septate, or less frequently three- to four-septate, large 

 conidia (28-38 X 10^11/a), roughly elliptical and mostly constricted at 

 the septa. Perithecia, averaging 150/a in diameter, appear as the winter 

 form of the fungus. They are sunken in the leaf tissue and have a 

 neck with a hairy ostiole. Asci 110-190 X 19-23/x. Ascospores are light 

 brownish, slightly swollen, 22-27 X 13/x, and commonly constricted at 

 the septum which divides the spore into two uneven cells. 



Symptoms. — The first symptoms are large, blackish, angular ne- 

 crotic areas on young leaves and frequently on shoots. These necrotic 

 areas are soon overgrown by olive-brown mycelia bearing conidia. 

 This stage of attack is followed by a total withering and blackening of 

 the above organs and a curving of affected succulent shoots in the form 

 of a hook. The whole symptom picture resembles frost or fire killing. 

 Complete defoliation occurs in severe attacks. 



Age of hosts. — Young poplars in nurseries and plantations are 

 especially susceptible. Areas with a high relative humidity, especially 

 along rivers, and with frequent spring rains provide the best condi- 

 tions for the development of this parasite. 



Possibility of spread. — Intercontinental spread of the fungus may 

 take place through shipment of unsterilized cuttings from infected 

 localities or through infected leaves that are occasionally put into 

 packing containers. Insects might also be fungus vectors. 



Range: The disease is particularly common in Italy, but it also occurs 

 in central Europe, Germany, France, and recently in Yugoslavia. 



Hosts: The following are reported as the most susceptible poplars: 

 Populas nigra, P. niara-italica, and different cultivars of euramer- 

 ican poplars. Italian clones proved to be highly resistant, 

 although under favorable conditions for the fungus, clone 1-214 

 was found to be intensely attacked (Yugoslavia). P. alba and 

 P. tremula do not suffer from this organism. Keduced and stunt- 

 ed growth, top deformation, and bushlike appearance of trees 

 are the most common results of the attack. Killing of young 

 plants, though rare, is possible under heavy infections. 

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