Hello Ann

This is magnolia scale on your tree. The large bumps on the branches are adults which protect the developing crawlers underneath the scale.

Wait for the tiny crawlers to emerge (sometime in August when GDD base 50 is at 1900-2000) and spray them. For small infestations, and a pollinator friendly approach, you can us a plastic kitchen scrubber to gently scrub off the adult scales before the crawlers hatch. See links below for more on these treatments.

If you used a spray in June it was too early, and would not have been effective. If you don't get full coverage, even at the right time, the tree will still have many scale insects on it. To effectively spray a large tree over 15 feet high you will need to hire a company which has equipment to treat large trees. The International Society of Arboriculture has a site where you can search for companies in your zip code- http://www.treesaregood.com.

August through September is usually active crawler time in Michigan and is the time to apply a spray to manage the crawler stage. Follow all label directions and precautions to avoid damage to the plant or to people.
You can monitor the correct time by observing the branches for crawlers, or by the Growing Degree Days for base 50 in your area. GDD Tracker is an online site used by professionals, and you may use it, too. See https://www.canr.msu.edu/news/use_gddtracker_to_schedule_applications_to_turfgrass

Pesticides and horticultural oils listed as controlling soft scales, including magnolia scale, are appropriate for controlling the crawler stage.(see links at bottom) Check the active ingredient on your insecticide and compare with those listed in the links at the bottom.

 The large adult scale 'bumps' that are easily visible will stay on the branches even though they are dead- they eventually dry up and fall off. If they are protecting live crawlers they should 'squish' liquid when crushed. Sprays will not affect these adults.

Trees under stress are more susceptible to insects and diseases. Be sure your magnolia is mulched in the root zone with 2-3 inch deep organic mulch, but do not let the mulch touch the trunk. During droughts in summer and fall water slowly with a soaker hose until soil is moist 7-8 inches down. Do not flood or let puddles develop.

Here are references with more details on magnolia scale insects:

https://bygl.osu.edu/node/1803

https://extension.psu.edu/magnolia-scale

https://entomology.ca.uky.edu/ef431