What might I look for? The soil pH is high, about 7.9. I have read that magnolias like 5-6. I've added sulfur to some areas to lower pH, mostly left this area with flowers to my spouse. The soil is subject to moisture, but seldom to never flooded. I've added mulch around the magnolia and a maple as one garden bed. I see what I think is anthracnose on a variety of species; apple, hazelnut, paw paw; that, being native, you might think would be fungus free. What could cause a leave to turn chocolate brown? Please see the additional pictures.

My wife says it's a star magnolia, not a lilly magnolia.

There are several things that could lead to chlorosis (leaf yellowing) and early leaf loss. Excess or insufficient moisture can be stressful for a tree. This can be the result of the level of water available in the soil or by damaged or malformed roots that are unable to transport water. Root damage can be the result of root rot, mechanical damage from digging, or roots that are intertwined and girdling the tree. These issues would all be below the soil, and aren't something I can tell by looking at a tree. There are also diseases and insects that cause the same symptoms. The lesions (dark spots) on the leaves could indicate a disease. There are both diseases of magnolia that cause leaf spots, but by pictures, I can't differentiate these. If you would like to have someone look at the tree in person, I would recommend contacting an arborist (TreesAreGood.org). If you suspect a disease issue, you can also submit samples to the diagnostic labs on campus (Plant & Pest Diagnostics (msu.edu))