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?

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.

            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.