We have a steep hill that is covered with mature Pachysandra that is dying. It is under a large Tulip Tree. This ground cover has been healthy for more than twenty years. During the last couple of years the leaves have turned yellow then the tips turn brown and curl up. The plant then dies. The problem seems to be spreading. Pachysandra is the only ground cover that is deer resistant enough to survive in our shady yard. How can we correct this problem. Thank you for your assistance.
This is a common problem with old pachysandra beds. You're seeing a disease called volutella. Here is information on what causes it and how to deal with it: https://extension.umd.edu/hgic/volutella-dieback-pachysandra-groundcover
You can probably diversity the bed with native ferns that are used to growing in the shade of large trees. They will tolerate dry shade. Hay-scented fern and lady fern are two tough ones. Deer do not eat them.
Do not plant non-native ferns such as painted fern or autumn fern.