The Magnolia looks like a Little Gem. I have one that has been in the gound also for about 6 years and it looks just like it. I don't think I have ever seen this variety of Magnolia that really looks good. That is not a fungus on the stems, it is lichens and while they do not live off the tree(they are epiphites-air plants)their presence does sometimes indicate a tree in decline. I haave no idea what to do for the tree. I have tried everything I can think of for mine, and I can't get it to grow and look good. Next step, take it out and replace with something else.

I planted 6 Little Gem magnolias two years ago. All of them have died. The DD Blanchard magnolias I planted at the same time have thrived. I've heard that Little Gems are not suited for our zone 10. My experience bears that out.

I have had one in the ground for almost 3 years now. It blooms like crazy, but has not grown much. Little Genms ARE SLOW growers for all those interested.

Magnolias prefer moist soil and less alkaline conditions than found in South Florida .
Magnolias grown in large containers stand a better chance of success further south .
For in ground planting ,
Professional magnolia companies use a soil drench called Safari with a drip line for steady moisture .
It allows trees optimal conditions to stay healthy enough for best growth .
If you cannot find Safari try Bayer Tree and Shrub .
Follow the directions on the container carefully .
Better to apply a slightly weaker solution twice a year than a heavy dose once a year .

Here is a link that might be useful: Small Trees for Miami Dade Landscapes

I have one that looks good and one that seems to have a bit of sooty mold on it.