Sometimes Powdery Mildew affects the plum much like it does the cherry, but it is far less common and of no economic importance. See Cherry and Apple, pages 177 and 113.
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 discussion, see Apple, page 96.