Extensive Dieback On A Shrub

From a photo it’s impossible to tell what caused this dieback although it has the look of a cultural problem not a disease. Cultural problems can be winter kill, herbicide damage, physical damage (string trimmers, rodent eating the bark, something falling on the plant etc), hot water from a hose or other situations that are not caused by insects or diseases. But no matter what causes the damage you see, your options are to remove the dead leaves and stems and see what happens, or to replace the plant. In general, when 2/3 or more of the plant is damaged as you see in this photo it might be the best thing to say good bye and plant something else. On the other hand, sometimes plants survive and thrive against all odds, so if you’re of the mind to “wait and see” the response would be to remove all dead material this year and leave what’s left over the winter. Next spring cut the living stems down by about a third and fertilize the plant, both of which will stimulate new growth. Resist the urge to do this now as it’s too late in the season to be stimulating new growth with fertilizer since it won’t be hardened off by winter.