Ask-a-Dave's-Gardener: Split Personality on New Zealand Tea Tree, 0 by DonnyK

DonnyK wrote:
I planted this New Zealand Tea Tree 14 yrs ago from a 1 gal container, it's now about 15' high and 15' wide. It has been healthy and very show ever since, until it developed its split personality this year. I has three main trunks, two going straight up on the left in the picture, and one that angles up to the right. Everything growing from the one on the right is still healthy and showy, but everything from the two on the left, while still with some green, appears to be dying with no blooms at all, and I have cut out a lot of dead branches from those areas. I don't see any pests, and all three trunks appear the same. Obviously all get the same water, sun, and soil, which has not been disturbed. I am trying to decide between cutting down both the affected trunks to try to protect the healthy one, or giving it time to recover. I would appreciate any thoughts on causes or treatment.