Question
Hello,

I have a large oak tree that I cut a 10" limb off about 10 years ago.  It has rooted out. I took my chainsaw and oppen the wound that would not heal. Drainall the water and tryed to cut out the root. I have sprayed it noe with a tree sealer, but should I fill the opening (quart size) or leave it open to dry???

Answer
Benefits from filling the cavity are questionable at best. Since the fill material will expand and contract at a different rate than tree wood it can create problems of its own. The strength of a hollow tree comes from the new wood produced after the injury, not from material used to fill a cavity. Remove hollow trees that appear weak and are likely to fall.

Sometimes the cavity will contain water. The old recommendation was to drill holes below the cavity so the water could drain. However, drilling holes will break the barrier that keeps the decay from invading healthy wood. If water has been present for one or more growing seasons, the tree has already adjusted.
When a tree is wounded, it uses its natural defense of compartmentalization to create a barrier between the wound and the rest of the tree. Recent research shows that it is better to leave the cavity open and take the necessary measures required to improve the overall health of the tree. A healthy tree has the strength to compartmentalize and wall-off decay.

I would Leave the area as is and spray the area with an insecticide for wood borers Merit is one of these type insecticides.