DANGEROUS INTERNATIONAL FOREST TREE DISEASES 113 



Perithecia of the Mycosphaerella stage occur on overwintered leaves 

 and on the cankered bark of 1-year-old stems. The asci, which contain 

 8 spores, are cylindrical, short stipitate, from 51-73/x X 12-17/x. The 

 ascospores are hyaline, one-septate, measuring from 17-24/x X 4— 6/*. 



This disease has caused serious losses on exotic and hybrid poplars 

 in eastern and central Xorth America. Although trees of all ages 

 are susceptible, the canker stage is restricted to the bark on younger 

 stems and branches. 



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 Xorth America it is common in eastern and central Canada 

 and the United States. In South America it occurs in Argentina. 

 Hosts: Salicaceae. Numerous exotic and hybrid poplars have been 

 found to be susceptible particularly those with black, balsam, and 

 cottonwood parentage. 

 Literature: 

 Bier, J. E. Septoria canker of introduced and native hybrid pop- 

 ^ lars. Canad. Jour. Res. C. 17 : 195-204. 1939. 

 Sarasola, A. A. Dos Septoriosis de las aiamedas Argentinas. Rev. 



Argentina de Agron. 11 : 20-43. 1944. 

 Thompson, G. E. Leaf spot diseases of poplars caused by Septoria 



musiva and S. popuh'cola. Phytopathology 31 : 241-254. 1941. 

 Waterman, Alma M. Septoria canker of poplars in the United 

 States. U.S.D.A. Cir. 947. 1954. 



Strumella Canker of Oaks 



J. R. Hansbrough 

 Forest Service, U.S. Department of Agriculture, Washington, B.C. 



Strumella coryneoidea Sacc. & Wint. (Imperfect stage). TJrnula 

 craterium (Schw.) Fries (Perfect stage). A perennial, usually non- 

 girdling stem canker of Quercus in eastern Xorth America. The first 

 symptom is a yellowish bark discoloration centered around a dead 

 branch or stub, usually with a raised margin and a depressed inner 

 zone, On the tightly adhering bark near the center of the canker, 

 small black nodules composed of interwoven hyphae are formed. 

 They produce no spores. As the infected area enlarges, two types of 

 lesions can result, target or diffuse, with frequent intergradations. 



Target-type cankers are most common and result from the forma- 

 tion of successive ridges of callus in opposition to the slow growth 

 of the fungus. These ridges form concentric circles around the base 

 of the dead branch at the canker center. Usually there is a pronounced 

 distortion or flattening of the cankered stem. The wood under the 

 canker face slowly decays and eventually the bark sloujrhs off. Dif- 

 fuse-type cankers occur when the fungus grows rapidly enough to 

 girdle the stem before callus formation takes place, usually on stems 

 that are under 4 inches in diameter. Water sprouts often appear be- 



