PLUM DISEASES 385 



Canada. Japanese plums are more liable to show the disease 

 than European varieties ; and it is possible that the latter group 

 is never affected. See Peach, page 289. 



CROWN-GALL 



Caused by Bacterium tumefaciens E. F. Smith and Townsend 



Bacterial galls occur on the crown and roots of the plum as in 

 the case of other fruit-trees. These enlargements are less com- 

 mon on this host than on the apple and peach. See Apple, 

 page 108. 



POWDERY-MILDEW 

 Caused by Podosphcera Oxyacanthce (Fries) De Bary 



Sometimes powdery-mildew affects the plum much like it does 

 the cherry, but it is far less common and of no economic impor- 

 tance. See Cherry and Apple, pages 177 and 113. 



ARMILLARIA Rooj-RoT 



Caused by Armillaria mellea (Fries) Quel. 



The plum is susceptible to a rotting of the roots which in many 

 cases is caused by Armillaria mellea. In the Pacific Northwest 

 prune-growers have been losing trees on account of this disease 

 for several years. This root-rot is said to do more damage to 

 the prune than to any other fruit in the State of Washington. 

 Likewise in some sections of Oregon, particularly in the northern 

 part of the Willamette Valley, Armillaria root-rot is a very 

 serious menace to the prune industry. For a more detailed dis- 

 cussion, see Apple, page 96. 

 2c 



