Question

Oak tree injury  

V and bark damage   This enormous oak tree has a cavity that concerns us.  A tree trimmer recently suggested that we cut a V in the tree to drain
water from it and that it would heal itself.  Now we wonder if
we have made a mistake.  Is there anything we can do to help it
and do you think, at this point, the limb is in danger of coming
down, especially during a hurricane or high wind.  I will attach
pictures.  There is also some damage to the bark that appears to
go deep below the V to the left.

Answer
The damage and problem with the tree is the v cut. Never never let a "tree trimmer"do anything BUT trim trees. This one I would not let near my tree. He does not know or understand the growth of trees.

The oak is hollow (there is a branch stub above the cut that looks to be open and hollow. That would mean the decay fungi has grown up the trunk at least to that point. But do not worry about the decay fungi. The tree has the capability to wall off the fungi and keep growing. The living cells of a tree are just under the bark and rest is woody cell that are dead. The decay fungi infects the woody cells and over time can hollow out a tree trunk. But the strength of the trunk will hold the tree up for many, many years. IF one of the upper branches break off and the end near the trunk is hollow then you might want to watch the tree since an upper limb could fall on your house. But this does not look like the case with your tree. I would fertilize the tree this fall with 1 lb of 10-10-10 fertilizer per inch of trunk diameter scattered around the tree and watered in good. This will increase the overall health of the tree. I would do this each year.

Not much now that can be done about the v cut. It will allow more decay fungi to enter and could allow an insect called a borer to infest the tree. I would spray the area with an insecticide called Merit. This will prevent borers from entering the wound. The cut does not look deep enough to drastically effect the strength of the branch. So it should be Ok in a wind storm. But it is weaker than before the cut.

I hope this answers your questions. IF you are seeking tree advice use a service who has a certifies Arborist or contact the Forestry state agency and ask advice from their Forester.