Question
QUESTION: New in past few weeks:  black stain on lowest and major horizontal limb of huge, beautiful ~40 yr. old carrotwood, centerpiece of my parents' back yard in L.A. Black sap oozing up out of conical hole ! 2 ft. from trunk, on upper surface. Called arborist.  I don't live near there.  He phoned, said thinks it's slime flux, we should drill all the way through that major limb, vertially, and let it dry out. I just okayed, not wanting to risk loss of that limb unless essential, or even worse, risk of loss of tree. I asked if it could get into phloem and kill whole tree.  He said that's unlikely.  Are we doing the right thing?  I'm a tree lover, responsible for invalid parents' affairs, extremely grateful for guidance. Thank you very very much!

ANSWER: If this is a certified arborist I would take his word since he has seen the tree. It does sound like slime flux.

Slime flux is the name given to the oozing or flowing liquid that is often seen during the heat of the summer on the trunk, large limbs, or basal roots of oak, elm, maple, apple, yellow- poplar, birch, hemlock, and willow. It is usually more common on large, older trees than younger ones.

Slime flux is what you see; however, it is caused by a condition inside the tree called wet wood. Wet wood is caused when bacteria invade a wound or injury caused by anything from construction damage to lawn mowing. This invasion, not the injury, is the good part! The bacterial growth creates pH and micro-element conditions in the wood that are undesirable for the development of wood decay organisms. In other words, wet wood is a defense against decay and not the fungi that might eventually cause a cavity to develop.

As time passes, the fermenting wet wood-causing bacteria produces methane gas which pressurizes the fluid in the wood under the bark that has grown over the injury. When enough pressure is created, the gas causes the wet wood liquid to ooze, flux, or bubble through the bark. Once in the oxygen-rich environment on the surface, this odorless and colorless or tan liquid darkens. It may or may not be colonized by yeast-like fungi. If the yeast-like organisms colonize the ooze, they grow and produce a foul, yeast or alcoholic smell. Then the flies, hornets, wasps, and sap beetles begin visiting and feeding on this brew of foamy, frothy, fluxing, fermenting slime.

Wet wood or slime flux will not in itself kill a tree. The fluxing is an outward sign of some type of previous injury to the tree. Whether the tree lives or dies will depend on the extent of the previous injuries and the amount of stress to which the tree has been subjected. If fluxing continues for a long period of time, the flow of liquid can discolor the bark, kill moss and lichens on the bark, or kill grass at the base of the tree.

Avoiding stressing the tree further and providing care that improves growing conditions are the best things you can do for a tree with slime flux. Depending on how much gas the wet wood is producing and how well the tree closes the wound, the fluxing may or may not be recurring.

If the flow, smell, or insects become objectionable, particularly on a tree near the front door or beside the patio, periodically flush the area with a stream of water or very diluted solution of household bleach and water. This will lessen the smell and discourage the insects from congregating.



---------- FOLLOW-UP ----------

QUESTION: I can't thank you enough for your generosity in providing this extremely helpful background information.  Could severe pruning have weakened the tree, setting it up for the wet wood problem?
I am very careful about whom I hire to prune trees at my Mom's house or my own.  But once someone who had been good before sent in a crew he did not supervise and they pruned this tree so brutally it had few leaves left to photosynthesize and I was grief stricken when I saw it, wondering if it would survive.  It is fully leafed out and looks wonderful, about 2 yr. after that drastic pruning, so I had thought we'd dodged a bullet.  That is the only thing I know of that constitutes "damage" over the course of this tree's long life.
And yes, I will definitely thank you by rating you Expert of the Month.
With my deep appreciation as a tree lover who tries to take good care of trees for which I'm responsible,
Norma Jean

Answer
No pruning would not have caused the problem it is really not understood why some trees get slime flux but other do not. When you select person to work on your trees I would check to see if they are a certifies Arborist OR at least get a recommendation fro the State Forestry agency. They should know whop is good and who can do a bad job. Here is the web link to the Organization that certifies the Arborist.

http://www.isa-arbor.com/findArborist/findarborist.aspx