My magnolia tree has an open hole on the main trunk where it had been trimmed many years ago. It never closed up , how do I protec
t my tree from anything infiltrating it’s health through that large hole? Magnolia tree in middle CA. Trunk is around 6ft. In diameter.
No photos came through so we can only give general information.
For a large tree with a significant cavity, it is best to consult with a certifed arborist to determine risk for structural failure based on solid wood vs decayed area and potential targets if the tree were to fail structurally.
Other than risk assessment, there is not much you can do to suppress advance of the wood decay within the cavity, except to keep the tree as healthy as possible with good soil and water management.
Filling and draining cavities is an obsolete practice for professional arborists.
The tree has natural defenses to resist advance of decay. You can prevent the harboring of animals and mosquitos with screening over the opening.