I have a large, hitherto healthy purpleleaf sandcherry. This spring a good-sized part of the plant is devoid of leaves, although some appear to have sprouted near the base of the main branch. The rest of the plant looks good and flowered. I am worried because the same sort of thing happened with our Newport plum tree; it looked healthy one year and the next year it was completely dead! I'm concerned that there might be a borer which is not readily visible, or am I over-reacting?