On Jun 11, 1:16?pm, "Charles T. Smith" wrote:
We bought and planted a tree that was called an "American Oak" about 3
years ago. It's currently about 3 - 4 cm (2 - 3 inches) in diameter.

A few days ago, I discovered a hole in the trunk, about 170 cm's from
the ground (under 6 ft). The hole itself is about 1.5 cm's in diameter
(just under an inch). A wire detected that it went about 15 cm up and 4
cms down (about a foot up and a few inches down).

After probing with the wire, I looked away for an instant, and then had
the distinct impression that I saw something out of the corner of my
eye pop its head out of the hole for a fraction of a second. I wasn't
able to get it again. It looked like a huge worm or something. Or maybe
it didn't happen. But something made that hole.

The hole occupies about 20% of the diameter of the trunk.

My question: will the tree grow in respect to the size of the hole, so
that the hole becomes insignicant, or will the hole "grow" with the tree?

Should I cut it down now instead of pealing it off my house later?

Should I fill the hole with anything?

Any thoughts will be appreciated.

Sounds like a tree borer. You probably did see it. I would try
standing guard duty for a while and perchance it will emerge again and
you can stab it with a barbed stick and yank it out. Also being such
a young tree is in your favor becaue it can't be very deep as it could
in a much larger tree, so there is probably just the one rather than a
colony. If I had no luck in grasping the borer I would attempt to
flush it out with a strong jet of water from a garden hose. Once it's
out there is no reason you couldn't pack the hole completely, cement
will work. The tree will heal and within 2-3 years you shouldn't even
be able to find the remnants of that hole. But more importantly keep
watch that more borers don't attack that tree or other trees as they
are likely in your soil. You probably should adhere to a regimen of
the proper insecticide applications.

http://www.ext.colostate.edu/Pubs/insect/05530.html