recent transplant ==>>>> one has to presume that a vast majority of plants come disease free from a seller ... and disease just doenst usually happen that fast ... but if they do.. its becasue the plant is severely stressed .. but treating the disease.. doent not help ... the stress and as far as i am concerned ... leaf color change from soil deficiencies.. do not happen that fast ... so i would call it all transplant shock ... how big was the transplant.. how did you plant it ... give us some relevant facts ... ken ps: maybe we should discuss GA clay.. and how you plant a shrub in clay ... see link for a primer .. rain and a clay cauldron that doesnt drain is a nightmare ... are you in that nightmare????.. see link about clay Here is a link that might be useful: link

They do best in medium to light shade. Create this condition and the plant has a chance. Shade from about 10-11 a.m. till sun set.

Any spraying going on nearby? It's odd that the leaf has a section (near your ring in the photo) which seems unaffected by the scorch or aerosol as though shielded by a leaf above. Still, the leaf looks a sickly yellowed green and brown dessicated areas seem to be heavily nearest the veins. Where you planted this Japanese magnolia, any chance there is or was a black walnut tree within 25' or so? If its not something aerosol, not something you can detect that is insect caused or insect spread like fungus or blight then the only thing I can think of is systemic toxins in the soil (juglone). How big is this shrub? Can you lift it and pot it up while you give it some TLC before re-planting in mid-late fall?

I don't about this variety of northern/deciduous Magnolia but never seem to have issues with the northern/deciduous "Tulip Magnolia" (Magnolia x soulangeana) or "Star Magnolia" (M. stellata) and my summers are pretty torrid. I did once have a "Jane" but it died. This year, my Crape Myrtles looked like the above pic. It was just a very humid summer for lots of us in the East/Southeast, I guess (as they say, not the heat but the HUMIDITY). As for treatment, leaves will soon be falling off, so I am just hoping for somewhat less humid season next growing season. Good luck!