168 DISEASES OF FRUIT TREES 



upon the twigs and branches and peculiar light brown spots 

 upon the leaves. It works later in the season than the scab, 

 necessitating, where serious, one or two sprayings after the last 

 spraying for scab. 



Cankers. — There are a number of diseases which attack the 

 twigs, branches and even the trunks of apple trees (and less 

 frequently of pears and quinces), producing ugly roughened 

 brown areas. Sometimes the diseased section is very well de- 

 fined with a distinct line marking its boundary where the dis- 

 eased tissue has shrunken and broken away from the adjoining 

 healthy tissue. In other cases, as the European canker, there 

 are many concentric rings or folds where the tree has repeatedly 

 attempted to heal over the wound and each time the fungus has, 



Fia. 72. — Apple canker. There are several different diseases which pass under the general 

 name of canker and some of them are quite serious. 



during its season of rapid growth, gotten the upper hand 

 (Fig. 72). 



Treatment. — These cankers vary greatly in the organism 

 which causes them and in the appearance, but the general line 

 of treatment is much the same. There ai-e three ways of fight- 

 ing such diseases. 



First, all affected twigs and branches which can be spared 

 should be cut out and burned. 



Second, in case the branch is too valuable to be spared, or 

 in the event of a canker spot on the trunk, the diseased tissue 

 should be cut out carefully and then the wound painted over 

 as in the case of wounds made in pruning. For the preliminary 

 work of cutting out, a light, sharp hatchet will be found very 



