MAPLE DISEASES 



229 



fungus. The spores from these structiu'es are disseminated by 

 the rain. It is to be expected that perithecia with ascospores 

 are formed in the leaves on the ground during the winter. 

 The twigs have not been found affected. This disease is 

 similar to the leaf- and twig-blight 

 of sycamores described on page 333. 

 The control measures are the same 

 for both of these diseases. 



Canker 



Caused by Nectria cinnabarina Fries 



Maples are commonly affected by 

 this canker. Other deciduous trees 

 may also be attacked by this disease 

 but it never assumes great impor- 

 tance owing to the causal fungus being 

 only weakly parasitic. Twigs, small 

 branches and young trees may be 

 killed by the girdling action of the 

 fungus. 



Symptoms. 



Small depressed dead areas of bark 

 around wounds or branch stubs are 

 the first evidences of the developing 

 canker (Fig. 40). Flesh-colored or 

 pink hemispherical bodies are pro- 

 duced on the dead bark. Later the same pustules become 

 chocolate-brown. If the fungus continues to spread, rolls of 

 callus are formed around the affected area each year, until an 

 open canker is produced which may girdle the limb. The 

 mycelium grows most luxuriantly in the sapwood, causing a 

 dark greenish discoloration (Fig. 41). The bark adjacent to the 



Fig. 40. — Nectria canker on 

 maple. 



