Be Careful of Misdiagnosis of Sooty Canker

Q. Our flowering plums have been infected by what was diagnosed as “sooty canker” disease.

Sooty canker on Apple

They were treated by arborists but the blight continues. Infected limbs were cut until one of the trees needed to be removed entirely. I am advised this blight has become epidemic in Las Vegas Valley. Is there a solution to cure or at least treatment for sooty canker?

A. Be careful on any diagnosis of sooty canker. There are a lot of natural things that can look like it and if you've never seen it before or don't have much experience around it, it can be easily misdiagnosed.

Sooty canker on poplar

Sooty canker disease causes limb dieback and the bark of the dead limb to peel away revealing a black, sooty powder on the wood. When you take your finger and rub against this black powder it will come off on your finger and look just like soot from inside your chimney.

There are other natural black “powders” on limbs which will also rub off on your finger. But sooty canker is jet black on your finger and unmistakable once you see it. I will post a picture of sooty canker on my finger on my blog so you can see what I’m talking about.

Beginning of sooty canker on Mulberry

I disagree, it is not an epidemic in Las Vegas. It attacks a small number of trees every year at about the same rate for the past 30 years. Many trees can become infected but we see it most frequently on Mulberry and Poplar (cottonwood) and occasionally on Ash and Elm.

I don’t remember seeing it on truly desert trees such as Mesquite, Acacia or Palo Verde.

It can be spread easily on pruning equipment if the equipment is not disinfected between cuts and between trees. 

Be very careful when this is diagnosed. If a limb is dead, it is dead and must be removed. We don't want to be removing limbs with the wrong diagnosis.