Thank you for your question.

This could be leaf scorch, sun scald, and/or powdery mildew. However, we have been receiving many questions this season about scale infestation on magnolia. For me to provide you a complete answer, I would like to be sure this is not true for your tree.  Here are the symptoms that characterize a scale infestation.

1).  Elliptical brown or white bumps on branches;

2).  Leaves have a sticky residue on them;

3).  Sticky fluids dripping from the tree;

4). Large numbers of wasps, bees, flies, etc. flying around the tree.

See:

https://northerngardener.org/facts-magnolia-scale/

https://apps.extension.umn.edu/garden/diagnose/insect/trees-shrubs/not-obvious/magnoliascale.html

https://extension.umn.edu/garden-and-home/yard-and-garden/yard-and-garden-insects/scale-insects

Could you please examine your magnolia tree and get back to us to indicate whether any or all of these scale symptoms are present?  If present, take pictures of the branches showing the bumps.

Many thanks.  Looking forward to your reply.

Thanks for your response.  Unfortunately I am unable to open your pictures.  They must be in png or jpeg format.  Could you please try sending them again.

Many thanks.