Sudden die off of Smoke Tree


I planted a Smoke Tree in my front yard in the Dufferin and Bloor area of Toronto about 10 years ago. It has done tremendously well, and is probably close to 30 feet tall..absolutely spectacular when in bloom. It is in a south-facing location with full sun, and can be dry..but usually Smoke Trees like that! I water when it’s very dry.

It is a multi-stemmed tree and last summer sections began to die off in rapid succession. By August last year only one section remained alive. When the sections died, the leaves just shrivelled up and turned brown within a matter of weeks. This spring there is one small section in leaf bud, but the buds look small, and I don’t hold out any hope for it.
I had an arborist in to look at it last summer, and he didn’t really have any ideas. He suggested that perhaps the roots were strangling other sections of roots underground? When I google these symptoms in a Smoke Tree, I come up with verticillium wilt as a possibility and am wondering how I know for sure.

We will have to take this tree out and replant, and if the soil if infected with this fungus it will affect what I can plant. For example, if I can’t have a Smoke Tree, I’d love to plant a magnolia…but read that they are also susceptible.

The only other tree in the yard is a Green Ash (City tree) which is so far unaffected by Emerald Ash borer. From what I read, they too can be affected by this wilt though, so I’m wondering if it can spread through the soil, and if the Ash tree is at risk.

Do you have any suggestions/input as to a diagnosis, or how I can get the soil tested? Or how likely it is to affect the next tree I plant. We’ve lived in this home for 25 years, and I’ve had no similar issues.


Thank you for contacting Toronto Master Gardeners.

That was a stunning Smoke bush, Cotinus sp. I am sorry for your loss.

It is not possible for me to diagnose the problem with the information I have. The arborists would have been in the best position to give you that information. You could go for a second opinion if you were not happy with the first arborist. You can look for certified arborists at

There are a couple of possibilities that can be looked at. If there has been any construction around the roots of the tree in the last few years you can see the effects start several years later. The roots spread out quite far ( well past the trees drip line) so it may not be immediately obvious that it would be affected.

If you send soil samples to Guelph University they can test for soil pathogens.  This would allow you to confirm your suspicions of Verticillium Wilt. 

If you do have Verticillium Wilt then you will need to replace the tree with something resistant to wilt. The fungus lives in the soil and it is not possible to eradicate it.

The link I have attached here shows plants that are susceptible to Verticillium wilt.

Some possibilities for replacement maybe a Dogwood, Cornus sp., or Serviceberry, Amelanchier sp. both of these have resistant varieties and will give you blooms and come in similar sizes to the smoke bush.

Good luck with your investigation.