Magnolia Scale Infestation
Your magnolia has been declining for quite sometime possibly years. An ashy black soot covers all of the leaves and it appears a swarm of sweat bees, wasps, etc. has taken up residence in your declining tree.
These are classic magnolia scale symptoms you may have encountered last year.
Go look at your tree now…you may see white/orange blotches over all of the branch tips that resemble mold patches…these are actually an insect pest called magnolia scale. Arguably the most effective method to control these pests is dormant/horticultural oil application in early spring (now) and again in late fall after leaves drop. Dormant oil smothers scale…and can harm the plant if applied during growing season.
Call a professional at Green Goddess LLC to help you save your prized flowering magnolia!