Like other stone-fruits the plum is subject to gum - flow when injured in any way. (See in this connection the discussion presented under Peach, page 303.)
In the Pacific Northwest a Bacterial Gummosis has recently been studied, and the cause found to be Bacterium Cerasi (= Pseudom,onas Cerasus Griffin). Particular attention, however, was given to it as it occurred on the cherry. The disease on the plum is similar to the Bacterial Gummosis of the cherry. This trouble on the plum is often erroneously called winter injury and sun - scald, but it has been shown that in most cases at least the action of the sun has nothing to do with the production of this disease. Cankers similar to those on the cherry are produced. Such lesions on the plum, however, exude noticeably less gum than those on the cherry.
Fig. 106. - Black Spot lesions on plum leaves; healthy leaf in center.
Hedrick, U. P. Prunes in Oregon. Gumming of the prune tree.
Oregon Agr. Exp. Sta. Bul. 45: 68 - 72. 1897. See further references to literature under Cherry, page 186.