My holly bushes have lost most of their foliage this winter. They were well established bushes, about 5 feet high, and have always been healthy. I even cut a few small berry branches for Christmas décor. They were fine in November, then I noticed most of the leaves have fallen and the bush is almost bare. This winter in northern NY has been extremely frigid and I did not really notice when the foliage started to fall. The bushes have been established for many years and I have pruned them once, about two years ago.