82 MANUAL OF FRUIT DISEASES 



inches or even larger. Affected branches are weakened and 

 often are broken by a heavy load of fruit. Stored fruit and 

 even fruits still in the orchard are rotted by the anthracnose 

 pathogene. 



Symptoms. 



The disease is known by the cankers which are produced on 

 the woody parts (Fig. 23). These are characteristically dark, 

 sunken, dead areas in the bark. On this account the disease 

 has been called black-spot canker, black-canker and dead-spot. 

 Cankers are found most abundantly on the younger branches ; 

 that is, those having a diameter of two to three inches or less ; 

 but larger limbs and trunks are not always free from such 

 lesions. On older branches the cankers are often more or less 

 superficial, not extending to the wood. But ordinarily on 

 younger limbs the bark and cambium are dead and the sap- 

 wood is discolored to a limited extent. 



The first evidences of this canker appear ordinarily from 

 November to January, depending on the season. The most 

 numerous and the most destructive cankers appear in November 

 and December. When first evident, the lesion is circular, 

 less than an inch in diameter, and the surface is not sunken. In 

 this stage the bark is discolored beneath the surface and has a 

 water-soaked appearance. Soon the discoloration extends to 

 the cambium and here it spreads out, often being more ex- 

 tensive than the surface discoloration would indicate. The 

 canker develops very little through the winter, but in March 

 and April it enlarges rapidly. As it enlarges its shape becomes 

 ellipsoidal,.and the surface sinks slowly. Sometimes the bark 

 shows concentric zones of slightly varying color. The margin 

 of the canker in the later stages of its development is limited 

 by a crevice, which is finally bounded by a callus. 



Toward the middle of the summer small, conical elevations 

 are observed on the canker. These burst through the bark 

 in a triangular or transverse manner, exposing a creamy mass 



