We have a very mature, large daphne bush(three feet high and six feet across) that has always been robust and come back from every type of natural disaster (as heavy snow and tree branches falling on it.) This spring one entire half of it began to dry up. We thought perhaps it was not getting enough water, so we watered it more. Now that side is completely shriveled up and the other side is not looking very robust. We have other daphne bushes in the garden nearby that are doing very well. Can you suggest what the problem may be and how to save the rest of the bush?