I've found that PL-Premium (polyurethane construction adhesive) to be a very durable, strong and water-proof glue for wood for all applications (indoor and outdoor).
I just filled a couple of holes on the trunk of a silver maple that have been formed by some sort of insect over the past maybe 6-months. The hole is in the face of a limb-cut that I made a few years ago and had painted with black pruning paint. I was surprised how deep the "rot" was - I was able to push the plastic dispensing nozzle of the glue cartridge all the way into down into the trunk.
So even though I've already done it, I'm wondering if anyone knows how well this stuff works at filling holes in tree trunks to prevent further rot and allow the tree to grow over and eventually cover exposed heartwood.