Magnolia oyama sieboldii

This lovely magnolia was beautifully shaped and seven-feet high, but our wet Vancouver Island spring following a cold snap or two in winter and last year's heat dome killed several large, structural branches. I removed the dieback and was left with basically a few long lower branches. It looked pathetic, but then got a heavy flush of new leaves, all growing from new vertical stems. Now a lot of the leaves seem to have a fungus of some kind (which has showed up in previous years). My question is: do I attempt to prune the magnolia or just leave it alone for a year? Will some of those verticals branch out or just behave like suckers? Regarding the fungal infection on the leaves: do I remove each leaf and discard it? I guess the larger question is, do these magnolias generally do well in our climate, or should I cut it down and replace it with something else. It is planted on a slight slope and receives afternoon sun.

 

Botanical name is Magnolia sieboldii. With oyama being a common name. How was it determined that the dieback was caused by weather conditions, and not instead something like bacterial blight? Show closer views of the rubbish on the leaves for best possible assistance here. An oyama magnolia I saw once at the Glades garden south of Vancouver was maybe 20 ft. across, perhaps the largest I have seen.

 

I just assumed the damage was weather related because the dieback was so severe. I’ve attached some closeups of the leaves. Thanks for your help, Ron.

 

The Seattle arboretum used to use a dormant spray on deciduous magnolias because of bacterial blight problems. Also there was chronic dying back of certain deciduous magnolias at the Rhody Ridge county park near Lynnwood, Washington until I suggested doing likewise. After which the affected trees immediately began to retain their growth and progress into larger sizes.

Magnolia-Bacterial Blight