12 



MASS. EXPERIMENT STATION BULLETIN 422 



Figure 11. Plum Pockets or Plum Bladders. 

 Note large misshapen specimens, in comparison with healthy plum at lower left. 



Photo courtesy of Plant Pathology Department. Cornell University. 



Black knot, another common disease of beach plums, is caused by a fungus 

 {Plowrightia morbosa). It develops in twigs and branches causing irregular 

 knots which may become quite large. The surest method of control is to cut 

 out and burn the knots. This should be done before January 1, since the winter 

 spores are formed from Januar\- to June. Spraying also helps in its control. 



Figure 12. Black Knot Cankers on Plum Twig. 



