Q.Why Are My Brugmansia Tree Branches Shriveling Up And Dying?
I have a pale pink 15 y.o. Brugmansia tree that blooms prolifically. However, within the past two years the old truck has become ulcerated and the branches drop leaves and shrivel up … they end up looking like witches fingers. As newer branches are developing, they look healthy … until they too become infected. I’ve asked many about this issue, including arborist, and no one has an explanation. I can’t find anything about it on line. I do not overwater (probably underwater) and live in a Coastal area. There are no signs of insects on the leaves & branches. At this point I’m thinking of cutting off the front part of the tree (the older, diseased area) and trying to see if the rear, newer area of tree will survive. Please help! Thank you.

Certified GKH Gardening Expert
It could be a fungal wilt disease. I would suspect that the new growth can't get adequate nutrients and water when the trunk is ulcerated and damaged. I would try to propagate a new tree from any healthy wood and start over.
https://www.gardeningknowhow.com/ornamental/trees/brugmansia/brugmansia-problems.htm
https://www.gardeningknowhow.com/ornamental/trees/brugmansia/brugmansia-diseases.htm
https://www.gardeningknowhow.com/garden-how-to/projects/rooting-plant-cuttings.htm