THE PLUMS 151 



Plum Pests 



Few fruit crops are so beset by enemies as are the 

 plums. Root, trunk, branch, leaf, flower, and fruit are 

 each attacked by insects or fungi or both, too often with 

 disastrous result. Yet the very fact of these attacks 

 makes the plums worth growing, for without these 

 various enemies the fruit would be so abundant as to 

 have little commercial value. 



The Black Knot has probably destroyed more plum 

 trees in the past than all other agencies combined. This 

 is a fungous disease which occurs upon wild and culti- 

 vated cherries and plums in the form of black, wart-like 

 excrescences upon the bark of twigs and branches. In 

 many regions its ravages are prevented by careful 

 watchfulness. 



Black Knot 



Black Knot, like other fungous diseases, reproduces 

 by means of spores. These appear in summer as a 

 velvety olive green coating upon the bark of affected 

 branches. They are scattered by wind and rain and 

 when they lodge upon the tender bark of other branches 

 they start the disease anew. Consequently one of the 

 first remedial measures is to cut and burn all Black 

 Knots wherever found to prevent the development of 

 these spores. It is also necessary to keep a sharp lookout 

 all through the summer for the swollen places on twigs 

 and larger branches that indicate new attacks of the 



