Why is my tree’s trunk oozing black stuff?

Why is my tree’s trunk oozing black stuff? This is a question we get asked often. Well, the answer is slime flux. Another name is bacterial wetwood.


Bacterial wet wood is a bacterial infection that attacks the trees trunk. As the bacteria multiply, it creates pressure within the trunk that escapes through the trunks bark and typically looks like a black oozing slime from under the bark.

Many times with bacterial wet wood during the warmer months, because of the sugars in the tree mix with the bacteria, it causes the sap to ferment creating alcohol.  Two years ago, one tree I saw had a particular bad case of slime flux. I observed multiple wasps and bees stumbling around and falling off of the tree drunk from the alcohol.   Her case was remarkable because I could smell the alcohol from 10 feet away. There was a lot of oozing out of this tree.

Bacterial Wetwood/Slime Flux Treatment- (Surface only)

Treating bacterial  wetwood is temporary at best. They used to recommend drilling holes within the tree in an attempt to relieve the pressure out of the interior portions of the tree. However this remains debatable as any sort of drill bit can potentially introduce bacteria deeper into the tree.

Either way, one accepted method  of treatment,  albeit surface treatment only,  is to simply mix one part  bleach to nine parts water and apply liberally to the trunk every couple weeks. Essentially this will kill off any bacteria on the surface and help  protect the trees bark layer staving off early delamination and introduction of decay. However, be aware that if your tree has bacterial  wetwood, likely  it will heavily affect the tree causing a decay pocket and perhaps weakening the structure overall. So you might want to mentally prepare that the tree  may eventually have to come down because of this infection.

11 thoughts on “Why is my tree’s trunk oozing black stuff?”

  1. Hi Mark,

    I’m an Arborist in CT and NY. Just found your site, good stuff.

    Like your honesty and professionalism….keep up the good work!

  2. Hello mark:
    I hope you can help me here I just cut a tree down that was causing some issues. I then ground the stump off , it was sapping horribly from the stump so that is why I ground it off. But now it is still sapping all over the place and ozzing down the driveway. What is going on and what do I do..

  3. Very helpful! I’ve used Bartlett over the last three years to help us save our trees. To no avail. We’ve lost 10 evergreen, a maple and a big oak trees and looking like we are going to loose more this year. There is black oozing at the base and oozing at different spots. Apparently the anaerobic bacteria is very contagious.

  4. On a recent camping trip there was a large limb left at our site. The limb had a very large hard (almost rock looking) growth, It would “chip” off so we burned the branch. When it got hot, black liquid started running out of the branch and it was like a blaze! It looked like a burning torch. What was this and is it dangerous_which is kinda late, but wondering if we should be worried from inhaling the smoke. Thanks for any info

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