If your cotton wood tree is "bleeding" an orange-brown sap that is attracting yellowjackets and other insects, it has a disease called bacterial wetwood or slime flux.
This condition often is present in older cottonwood, elm and willow trees. A bacterium that normally lives in the soil enters the tree through root wounds. As this organism reproduces, it moves into the core of the tree or right beneath the bark. Little oxygen is present in these tissues. As the bacterium grows, conditions become anaerobic (no oxygen) and fermentation takes place. The whole process yields gas, and pressure builds up. This pressure is relieved by the oozing or slime you see running or bleeding down the trunk. This slime often is odorous, attracting many insects.
No direct correlation exists between the death of branches and the bacterial wetwood. During hot weather, however, some branches may wilt and die through a combination of several factors, including bacterial wetwood, winter freeze damage or root injury.
Unfortunately you can't do anything to correct bacterial wetwood. Sometimes it just goes away by itself; at other times it is present throughout the life of the tree.
Bacterial wetwood indicates a tree is under stress. If the tree is old and in decline, you might want to consider replacing it.
For more information see CSU Factsheet 2.910
Photos: Judy Sedbrook
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010