Clear sap flowing from the wound becomes colonized with bacteria, darkens, and develops an unpleasant odor. The specific bacteria causing the dark color and odor are rarely identified. Identifying the Injury. In addition, insects are attracted to the wet area. Often the bark in the area of the slime flux separates from the tree bole and gives a hollow sound when tapped.
Bacteria colonize the sap causing the typical odor.
The bacteria-laden fluid is toxic to the bark and enlarges the wound with time. Removing bark from the affected area will reduce damage to an individual tree. Photo by Fred Baker Canker on Siberian elm.