wystery

Hope these images give you a better idea, the diseased part was on the lower left-most branch in the first photo. As for soil change, I don't believe so, unless you count applying mulch to the base of the tree in the past few years.

Thank you for your prompt answer, I really appreciate it! Do you know how I might identify what other factor it is that is affecting the tree? Especially airborne pathogen.

First time here! There's been a whiteish growth creeping down one of the branches of our cherry blossom tree. We decided to cut off the diseased part, and the wood was totally dead. I believe it may spread to the entire tree eventually, which is a shame for how beautiful our cherry blossoms are. Does anyone know what this is and how to treat it?