Hello Your magnolia has magnolia scale. The scale also produces a honeydew which is mainly sap that the scale secretes. I’m attaching an MSU Extension bulletin that describe this insect. https://www.canr.msu.edu/news/check_magnolias_for_magnolia_scale_now You will see in that article that controlling the insect depends on the stage of the insect. June to early July is the time to apply systemic insecticide which will move from the roots to the branches. The next stage in the insect’s life is the active crawler stage which occurs in Michigan in August through September when you can spray with a contact insecticide. You should not need to use the second application if you do the first. MSU’s Enviro-weather site has a tool which states when the crawlers are active. http://msue.anr.msu.edu/news/magnolia_scale_is_starting_to_appear_on_magnolias Always read and follow the instructions on the insecticide label for the best results. Finally, if your tree is too big for you to treat, consult a certified arborist. Go to http://www.treesaregood.org, the website of the International Society of Arboriculture to find an arborist in your area.