DAXGEROUS INTERNATIONAL FOREST TREE DISEASES 69 



developed fungicides are only possible in forest nurseries. A tree 

 which successfully resists Chondroplea populae has not yet been cul- 

 tivated. 



Range : Europe, Canada, North America, Argentina. 

 Hosts: On the susceptibility to this disease of various kinds of pop- 

 lars, Butin (1957) states the following: 



The available data in existing literature on various kinds of poplars 

 susceptible to this disease stress an increased susceptibility of those 

 trees belonging to the Aigeiros group. Of this group Populus cv. robusta, 

 P. cv. bachelieri, P. cv. eugenei, P. nigra, var. italica, and P. cv. verniru- 

 bens are obviously in grave danger, and P. cv. marilandica and P. 

 balsamifera-groui), but to a much lesser degree. P. alba, P. tremula, P. 

 tremuloides, and P. candicans are mentioned as resistant or less en- 

 dangered species. 



Literature : 



Butin, H. Untersuchungen uber resistenz and Krankheitsanfollig- 



keit der Pappel gegenuber Dothichiza populea Sacc. et Br., Phyo- 



path. Ztschr. 28 :353-374. 1957. 

 Die blatt — und rindenbewohnenden Pilze der pappel unter 



besonderer Berucksichtigung der Krankheitserreger. Mitt, aus d. 



Biol. Bundestanst. f . Land-u. Forstw. Berlin-Dahlem, Heft 91 : 



50-52. 1957. 

 Petrak, F. Uber die Gattungen Dothichiza Lib. und Chondroplea 



KleB. Sydowia, Ann. Mycol., Vol. X : 201-235. 1956. 



Leaf Blotch of Horse Chestnut 



Guignardia aesculi (Peck) Stewart (German term: Blatt rollkrank- 

 heit der Rosskastanie, Blattbraune der Rosskastanie). This disease 

 was minutely described by Stewart (1916). According to his report 

 it causes great damage to Aesculus hippocastanum and A. glabra in 

 America. ^ 



In recent years this disease has spread more and more in Europe 

 and caused considerable damage. The latest paper on leaf blotch 

 of horse chestnut was written by Petrak in 1956. 



The macroscopic symptoms may be summarized as follows: Red- 

 dish-brown blotches of considerable size appear and spread quickly 

 over the leaves, which then die. At the same time the leaves roll up 

 cornet -wise, which accounts for the German word for this disease, 

 namely : Blattrollkrankheit. 



Petrak also points out the fact that there are still some healthy 

 trees even in badly infected areas. By the propagation of these trees 

 the disease could be checked. 



Through microscopical examination of infected leaves, Petrak dis- 

 covered that loosely spread pycnidia of PhyUostictina sphaeropsoidea 

 (Ell. & Ev.) Petr. were contained in the blotches on the leaves that 

 were still green. In the dead leaves the examination revealed pycnidia 

 of Asteromella aesculicola (Sacc.) Petr. and the related perithecia of 

 Guignardia aescidi (Peck) Stewart. 



PhyUostictina sphaeropsoidea. Pycnidia: Roundish or broad- 

 elliptical 80 to 170/x, occasionally up to approximately 200/* in diam- 

 eter. Conidiospores 10 to 15/* long and 6 to 10/* broad. 



Asteromella aesculicola. Pycnidia: Mostly 40 to 80/*, conidiospores 

 4-6 X 1-1.5/* big; in some pycnidia even bigger: 5 to 9/* long and 1.5 to 

 2.5/* broad. 



