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



low the cankers. Small trees are killed but larger trees may remain 

 alive for several decades or until the tree breaks at the canker. 



The fungus rarely sporulates on living trees; however, if the tree 

 dies, and while it is still standing, sporodochia are produced abundant- 

 ly, both on the cankered area and beyond. They are dark brown, 

 rounded, powdery pustules, 1-3 mm. in diameter, bearing stout 

 branched conidiophores from the tips and sides of which are produced 

 irregularly globose to pyriform, brown, spiny conidia, 6.7-8.1 X 4.7- 

 5.8/>i. These conidia do not germinate. They are windborne but their 

 role in causing new infections is unknown. 



After infected trees fall, the Urnula stage is produced. The 

 apothecia, always attached to decaying wood, are common and con- 

 spicuous in early spring. They are up to 3-4 cm. in diameter and 4-6 

 cm. deep, black, leathery, rupturing irregularly. The asci are cylin- 

 drical, with 8 one-celled, smooth, hyaline ascospores, 12-14 X 25-35/x. 

 Ascospores are windborne and germinate readily within a few hours 

 after release from apothecia. 



Strumella canker is common but losses are not catastrophic. The 

 fungus spreads slowly, seldom infecting more than 2 or 3 percent of 

 the trees in an oak stand. Most cankers, however, occur on the first 

 12 feet of the trunk, seriously reducing or destroying the value of the 

 butt log. Wind breakage of cankered trees occurs frequently. Con- 

 trol is through sanitation — removing infected trees in weeding, thin- 

 nings, and harvest cuts. 



Prevention of intercontinental spread of Strumella canker should 

 not be difficult. Infected trees are distorted and the infected portion 

 is seldom, if ever, harvested and utilized for anything other than fuel. 



Range : 



In North America it is common in eastern United States. The 



fungus is reported as a saprophyte in eastern Canada, western 



United States, and one collection from Europe (Germany). Im- 

 portant only on oaks. 

 Hosts : 



Fagaceae — 



Quercus velutina Lam. 



Q. rubra L. 



Q. coccinea Muenchh. 



Q. ilicifolia Wangenh. 



Q. macrocarpa Michx. 



Q. marylandica Muenchh. 



Q. prinus L. 



Q. prinoides Willd. 



Q. palustris Muenchh. 



Q. bicolor Willd. 



Q. alba L. 



Fagus grandi folia Ehrh. 



Castanea dentata (Marsh.) Borkh. 

 Betulaceae — Ostrya virginiana (Mill.) K. Koch 

 Tiliaceae — Tilia, americana L. 

 Cornaceae — Nyssa sylvatica Marsh. 

 Aceraceae — Acer rubrum L. 

 Juglandaceae — 



Cory a glabra (Mill.) Sweet 



O.ovata (Mill.) K. Koch 





