It would take investigation but both species are quite susceptible to verticillium wilt.

Here is a link that might be useful: verticillium wilt

I think you are right. What's more worrisome is I have a young redbud growing close to the affected plant. I'll have to remove the affected branches right away. Thank you for your help.

That wilting may be related to water. If you are experiencing the lack of rainfall we are here, many of my trees are wilting from the heat and lack of soil moisture, or maybe too much water which can cause the same thing. With most diseases you would see other signs beside wilting.

Yes , sudden wilting is mostly caused by Verticilium because there are other healthy branches beside the diseased one, it means that the problem in vasucular tissues.

Well I had removed yet more parts of the tree as more limbs became affected. In fact the cut trunk showed dark circles and gummy sap. I'm afraid my beautiful royal purple smoke tree is a goner. It's been a very rainy summer coupled with some dry spells, so the fungus is probably going to be in the soil for quite a while. The area is also nex to my redbud, a rose and several boxwoods which I hope won't be affected. Keeping my fingers crossed.