Hello Mike,  Thank you for allowing me to help you with your magnolia scale problem.  There are indeed many ways to handle them.  This is called Integrated Pest Management.   IPM not only includes chemicals but also physical ways of dispersing them.  You can even squish them (not my favorite). Scrubbing them off is another way using a dish pad.  

The best time to spray with horticultural oil is: on first instar crawlers in late summer or early fall.  https://640whlo.iheart.com/featured/ron-wilson/content/2024-06-24-magnolia-and-tuliptree-scale-joe-boggs/

when is the best time to spray with dormant oil:  Dormant oils can be applied in October through November and again in March to kill the overwintering nymphs located on the stems.   https://ohioline.osu.edu/factsheet/ENT-61

Best time for Imidlacoprid systemic application is early may.  However you can spray it in late Aug or early Sept and reapply 10-14 days later.  https://hort.extension.wisc.edu/articles/magnolia-scale/#:~:text=Apply%20spray%20treatments%20in%20late,root%20zone%20in%20early%20May.
Here is another very good fact sheet on magnolia scale  https://bygl.osu.edu/node/1803