".... The limb was about 6 inches in diameter. I cut the stub at an
extreme angle so the water would run off. This creating an oval area about
18" by 8" of exposed wood....."

First thing I would do is to cut the remains off level with the trunk
(Vertical) to give the smallest area, you have created an area for the water
to hold on the cut wood, also it will take years for the tree to grow over
such a protrusion, so more chance of serious harm to the tree.


--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk