Kousa dogwood not thriving
I have a kousa dogwood that I planted eight years ago. It blooms every year but has not put out any new growth, and every year one or two more small branches die back. It gets full sun and I have been fertilizing with Holly Tone each spring. From the photo you can also see that the leaves are small (relative to other kousas I've seen) and have brown edges.
I thought it might be lack of water, as the tree is in a raised area that drains very quickly. Last summer I made an effort to give it a heavy watering at least monthly, even weekly in the hottest part of the summer, but this doesn't seem to have made much difference.
I showed this picture to someone at our local nursery and he thought it might be anthracnose, but it doesn't look like any of the anthracnose photos I've seen, which all show spots on the leaves. The leaves don't fall off or get any worse -- they just have the brown edges you see in the photo and stay like that all season.
Our soil tends towards heavy clay, though I did dig up the bed and mix in a fair amount of peat moss and compost when I planted the tree. A crabapple planted at the same time in the same soil nearby is growing very well.
Any suggestions would be greatly appreciated.