The symptoms you describe sound a lot like verticillium wilt, and viburnums are among the many many plants that are susceptible to it. There is little you can do except prune away all the affected limbs, keep it watered and fed, and hope for the best.

My smokebush was diagnosed with verticillium three years ago. It began to do just what your Mohawk is doing now. I thought I would have to remove it, but decided to wait. Now, I'm still not sure verticillium was the real problem because my smokebush rebounded and is beautiful now, but I've read that attacks of this disease can comeout of nowhere with years in between. After three years, I watch that shrub like a hawk looking for signs of wilt.

Good luck. It's a heartbreaker, that disease.

I lost a tulip tree to that a few years ago but the whole tree wilted and died within a few days. This is only affecting part of the shrub so I assumed it was something different. I'll read up on it some more. It's encouraging to hear that your smokebush is still alive. Thank you.

I"m told that curling leaves on my Mohowk (which by the way, my neighbors also get on this cultivar) are due to spider mites or aphids. Not serious if this is your problem. Insecticidal soaps should help.