52 MANUAL OF FRUIT DISEASES 



berry, oak, pine, rose, sumac, witch-hazel and others. In 

 the spring the pycnospores emerge from the pycnidia beginning 

 in April ; this discharge goes on throughout the growing-season. 

 The spores ooze from their pycnidia in coil-like masses ; the rain 

 and wind carrying them to the leaves, fruits and bark. In- 

 sects are not known to disseminate the fungus. Germination 

 of the spores occurs within six hours, the tubes entering 

 the various susceptible parts through wounds, except in the 

 case of young leaves which are penetrated through the uninjured 

 surface. Within a few days symptoms of the disease appear as 

 already described. Pycnidia, in which spores develop, are soon 

 formed on the affected organs of the apple. These spores are 

 carried to other susceptible organs throughout the growing- 

 season. Some of the spores may be disseminated to any of the 

 many plants previously listed. With the advent of winter the 

 fungus ceases its activities, and lives through the dormant 

 season in the form of mycelium and spores in the cankers. A 

 perithecial stage is known, but it apparently plays no promi- 

 nent role in the life-history of the pathogene. 



Control. 



The treatment of this disease consists in the eradication of 

 cankers and in protecting the susceptible parts by the use of 

 fungicides. 



The treatment of cankers may be followed along one of two 

 lines. The affected limb may be cut from the tree, or the 

 diseased bark may be removed. The grower must study the 

 problem and must proceed in accordance with the conditions. 

 The size and value of the limb and the extent of the infection 

 will be criteria. Small limbs, that is, those with a diameter 

 less than one inch, should in all cases be removed. It would 

 rarely be profitable to attempt to treat a canker on a branch of 

 this size. If the larger cankered limb is valuable because of its 

 producing powers, then the size of the canker must finally de- 

 termine the course to pursue. Smaller cankers on large pro- 



