It appears that your tree has Magnolia scale, caused by the insect Neolecanium cornuparvum.  They must have been on your tree unnoticed since last summer/fall. https://content.ces.ncsu.edu/magnolia-scale

While it is early for them to be active, it is not totally surprising with the recent high temperatures we've been having.  The insect has three stages: Crawler, nymph and adult.

The crawlers appear as tiny dark specks on the branches of the tree in the early spring.  They mature into nymphs.  The males will develop into small gnat-like insects with wings.  They seek out the wingless females to mate.  The females stay immobile.  As they mature, the females develp a convex covering that is elliptical in shape with a waxy covering. This is what you see on the branches.  The insects suck the sap from the tree and produce a sweet exudate called honeydew on the branches and leaves.  This honeydew attracts a black fungus called sooty mold which then grows on it.  The sooty mold is secondary and not what is causing the damage to the tree. 

Some potential controls for scale include pruning out the affected branches and twigs.  You can also try using a brush and gloves to lightly brush off the insects with care not to damage the tree bark.

Unfortunately chemical sprays, such as foliar sprays, are applied from August to the end of September to control the crawlers (the hatched magnolia scale eggs) so they will not be effective at this time.  However, you should apply this in the fall to continue control for next year. 

Another treatment is to spray with a dormant oil spray (available at home stores and nurseries) in the early spring.  It requires care not to spray buds and blooms and should be applied before the buds open, so it is also too late to use this treatment this year.  

This scale is a difficult problem to treat successfully and may require treatment over several years.  Currently, your only options for right now are pruning and trying to physically remove the scale. Sadly, one more option is to remove the tree.