Sound like Bark Split. Bark split is most commonly caused by an autumn frost while the sap is still high in the plant, or a spring frost after the sap has already started to rise. For this reason it is dangerous to feed nitrogen to a rhododendron or azalea that could stimulate growth through to autumn. Don't use nitrogen after mid-June. When the sap freezes, it expands and ruptures the tissue under the bark and splits the bark. For this reason always keep mulch away from the trunk of plants. Bark split damage can be treated with grafting wax to prevent fungal and insect damage. If left untreated, it is fatal.
{{gwi:386387}}

Boy,

That is too bad because I would hate to lose this tree. Do I completely girdle the trunk base with the grafting wax, or just where the exposed core meets the still-living bark?

(image below revels the extent of damage)

David

http://i233.photobucket.com/albums/ee262/davidfromdetroit/100_1172.jpg

The wax is to seal the exposed wood from insects and dessication. So apply the wax where there is damage and exposed tissue. If it is completely girdled, there is little you can do except bridge grafts. They are grafts that go from above the damage to below the damage. The other option is rooting cuttings from the part above before it dies.

Thank you Rhodyman - great counsel and I appreciate your insights,

David