Several shrubs and trees have died, slowly, over the last two / three years - viburnum, ornamental plum, mallow, japanese maples, fuschia - photograph shows fungus on the mallow, no sign of honey fungus fungi, bootlaces etc., - other symptom is deep cracking / splitting along branches. All are in the front garden and relatively close. Starts with die-back of parts of shrub/tree and continues. Any ideas or suggestions?