BLACK-KNOT 



173 



spring. The spread of the disease is markedly favored by cold, 

 damp weather in the spring. 



It may be controlled practically by a single spraying with 

 lime-sulfur at the winter strength applied just before the buds 

 break, or just as they are breaking, in the spring. 



Black-knot. This is another very striking disease and 

 attacks both the plum and the cherry, principally upon the 

 smaller branches but often upon both main branches and trunk. 



Fia. 74. 



Fia. 75. 



FIG. 74. A plum tree badly affected with black-knot. 



FIG. 75. The same plum tree as shown in Fig. 74 after the knots have been cut out. 

 It is possible to recover trees which are very badly affected if the knots are cut out and the 

 trees sprayed. 



The spores gain entrance to the tree during the spring or summer 

 and grow for a season entirely within the branch. The follow- 

 ing spring the affected part of the branch begins to swell and 

 soon the well-known knot develops. At first it is soft in texture 

 and light brown in color, but gradually turns darker and becomes 

 harder in texture. During late spring and early summer the 

 knot is covered with a velvety appearance, which is caused by 

 the production of summer spores. Later these disappear and the 

 surface becomes hard and roughened. 



