Black Streak on Mesquite Tree

Q. I have a 30-foot tall Chilean Mesquite tree that looks nice and healthy but has a 2-foot long dry black streak on its trunk. What is it and what’s the problem?

Black discoloration of mesquite trunk from my pictures

A. These dark streaks on the trunk are a common occurrence on mesquite, particularly if it had been pruned in the past. In common vernacular, the tree “bled” after it was pruned. If your tree otherwise looks healthy, then there is nothing to worry about.

Wetwood aka Slime Flux  

            Mesquite gets a minor bacterial disease problem called wetwood, a.k.a. “slime flux”, which causes a similar staining on large limbs and the trunk. But the black stain is constantly wet and “smelly”. Slime flux is a bacterial infection deep inside the tree which causes a wet “yeasty” oozing to flow from limbs that attracts flies. It’s spread from tree to tree by lots of things including “tree trimmers” that think they are arborists. It’s not a lethal disease problem for the tree, but it may cause owners some angst.

Slime flux bacterial disease on African sumac.

            I have a picture of a mesquite tree with a black streak on its trunk on my blog. I will repost it for you to look at and compare.