Stressed Chitalpa Tree

I reside in Arizona where Chitalpa trees are ubiquitous to many residential landscapes. For the past two springs mine have emerged from winter dormancy with lush green foliage and prolific blooms only to turn yellow and defoliate in a matter of weeks. One landscaper cited under-watering, another over-watering, and a certified arborist blamed a bacterium destined to kill the tree in a matter of weeks. We have emerged from another spring with the same scenario repeating. Given the contradictory diagnoses of supposed professionals, I would be grateful for other opinions.