My Magnolia has a central stem with rot. Should I go extreme and prune it hard to save the plant? I noticed an earwig in the hole last year too.
Check the the roots where they join the stem are not more than 3cm deep. If they are deeper than 5cm, lift the plant, taking a large root ball, and re-set it with the rootball just at soil surface level. Make sure to water in a dry spell and stake it if necessary.