British Columbia: Magnolia Grandiflora massive leaf drop

My large 30' Magnolia Grandiflora 'Saint Mary' which I acquired 7 years ago as a quite large specimen from a local nursery has suffered a massive leaf drop this spring. While some leaf drop is common each year, now after a few good spring wind storms in Vancouver, the tree has lost over half its leaves and the remaining are looking pathetic with many branches totally denuded. Many of the leaves that have fallen and some remaining leaves that will probably fall soon have partially turned brown as if they have lost most of their clorophyll.

Until this year, the tree always had a full compiment of large fat healthy leaves and wonderful large creamy flowers, but it now looks awful. Only a few healthy fat green leaves remain on the bottom branches. I first noticed some minor branch denuding and leaf drooping in the late fall/early winter, but the tree is now a shadow of its former self. Many of the bare branches do seem to have budding leaf spikes at the tips however.

It also has large areas of redish "underbark" along the main central stems whith the older outer bark sluffing off when rubbed -- don't know if this is normal bark renewal or not.

 

Probably a pathogenic infestation of the roots, maybe honey fungus (look for Armillaria rhizomorphs on the lower trunk and crown). Or some equally destructive development.

 

Thanks Ron, I'll be poking around the base of the trunk looking for rhizomorphs tomorrow.