Thank you for contacting Ask Extension. This year has been really bad for magnolia scale. If the pesticide company sprayed your magnolia recently, the reason you have not seen any improvement is because it is the wrong time of year to spray. Scale has a waxy coating and sprays cannot get through that surface. But if you spray between September to early October, that is when the crawlers are moving. 

So here is how to take care of the Magnolia Scale. There are two methods in dealing with a heavily infested tree. The first is to buy a product with the active ingredient imidacloprid or dinoterfuran. You will mix these up, according to the label instructions, to make a drench to pour around the tree. The second method is to spray your tree when Magnolia scale is in the crawler stage. You will want to look for small reddish crawlers that emerge in the middle of September and early October. You will use a horticultural oil, sometimes called Neem oil, to spray over the crawlers which will suffocate them. You will want to do another spraying in early spring after the last frost, but before the buds have opened. You might have to spray more than one time to get rid of the scale. And it will take a few months before you begin to see any improvement, but if you are diligent then you can rid your plant of the scale. 

I have included several publications to help you with what to spray and when.

https://www.canr.msu.edu/news/why-is-sap-dripping-from-my-magnolia-tree

https://ohioline.osu.edu/factsheet/ENT-61

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

If we can be of further assistance, please contact us.