82 



POPULAR FRUIT GROWING. 



fore the buds open. Later, sprayings of Bordeaux mixture may 

 be necessary if the weather is rainy. The object of these spray- 

 ings is to kill the spores of the disease which are found on the 

 bark. 



Black Knot or Wart of the Plum (Plowrightia morlosa). 

 This manifests itself by wart-like or knot-like growths appear- 

 ing on the smaller limbs as well as on the larger branches and 



sometimes even 

 on the trunks. In 

 sections of the 

 country where 

 the European 

 Plum (Prunus do- 

 mestica) is grown 

 this is one of the 

 most serious ob- 

 stacles to its suc- 

 cessful cultiva- 

 tion. Our native 

 plums are not 

 often destroyed 

 by it, but it some- 

 times causes seri- 

 ous injury to 

 them. This knotlike growth is spongy and of a black color. 

 Upon examining it with a microscope it is found that the surface 

 has many little cavities that contain the spores by which the 

 disease spreads. Spores escape from the knots during the late 

 winter or early spring. 



Remedies. Upon their first appearance these swellings 

 should be removed and burned, if they are on the smaller 

 branches where it is practicable to get them off. If on the trunk 

 or larger branches where the branch cannot be cut off, they 

 should be cut out as much as possible and painted with thick 

 Bordeaux mixture. Where trees are badly infested they should 

 be removed entirely. This same disease also grows on the wild 

 choke cherry and black cherry and, if abundant on them, their 

 removal will make the extermination of the disease easier in 

 the nearby plum orchard. 



Fig. 34. Plum pockets as they ap- 

 pear on the tree. 



