u/Jamoncorona

Hi all, I have been growing a number of Nanking and romance cherry bushes to make a sorts of hedge fence around my front corner yard, but in the last couple of years I've noticed some of my cherry bushes started showing dark barking around the tips of the branches, and this spring I realized that two of the nanking bushes are now dead.

Any ideas how to treat the remainder of the bushes? They're lovely and super productive, and I live across the street from an elementary school, so during fruit season the kids like to get a snack while they walk past. I would like that tradition to continue.

Halp?

edit: I realize bushes are not trees, but I'm hoping your expertise also spans the smaller sized woody plants. thanks for any help!