Q: What can we do to save this big snowball bush?
A: I think the damage is caused by squirrels enlarging the holes made by sapsucker woodpeckers. It’s serious but I don’t think you can do much to deter the squirrels. If you wrap the limbs with chicken wire, they will just go to other spots.
Another possible culprit: rats. Someone approached me at an appearance and said she had seen rats chewing the bark off her red maple.
That said, I have an experiment for you to try. Get some Repellex (click for sources) and use it under the bush.
If it works, please let me know!