230 



MANUAL OF TREE DISEASES 



affected sapwood dies and the mycelium invades the dead bark, 

 forming its fruiting-bodies on the outside. The canker develops 



slowly and may at any time cease 

 to enlarge. The exposed wood is 

 then finally o^Trgrown by the callus. 

 This canker is especially common 

 in severely wounded or recently 

 pruned trees. 



Cau,?e. 



The canker of maples is caused 

 by the fungus Xectria cinnabarina. 

 Spores are borne over the outside of 

 the flesh-colored pustules during the 

 summer. After the pustules be- 

 come chocolate-brown, perithecia 

 are formed which produce asco- 

 spores. These spores are matured 

 over winter and produce infection 

 in wounds in the sprmg. 



Control. 



The cankers can be removed by 

 surgery (see page 3.51). AU dead 

 bark and twigs should be cut away 

 at the same time, since the causal 

 fungus occiu-s e^•er^-«■here as a com- 

 mon saproph}i:e. Pruning wounds should be at once protected 

 by a wound dressing (see page 348). 



Fig. 41 . — Cross and longitudi- 

 nal sections through a Nectria 

 canker on maple. 



Refehexce 



Sehreiik, Hermann von, and Spaulding, P. Neetria cinnabarina. In 

 Diseases of deciduous forest trees. U. S. Dept. Agx. Bur. PI. 

 Ind. Bui. 149 : 21-22. 1909. 



