One "trunk" on my burkwood viburnum is dying. The rest seems fine. Another trunk didn't leaf out this year, and we cut it down. The bush is about 20 years old. The bush is in partial sun, next to a deck and its stairs.The soil is not compacted and hasn't changed. I don't fertilize the bush. It seems to flower fine without fertilizer.
Viburnums can get botryospheria canker. It is stress related, which means that when a plant is under stress (from drought usually) it will be more susceptible. It affects scattered branches which require removal. Here is a good link from Rutgers about care:http://www.steveslandscaping.net/PDFs/Plant%20Canker%20Diseases.pdf