Greetings Paul:
Depending on the stage of infestation and how many years your tree has been plagued by this scale, you will likely be able to treat your silver maple with a timely (i.e., during the crawler stage) application of insecticide.
Please refer to the following publication from University of Wisconsin Extension:
http://learningstore.uwex.edu/assets/pdfs/A3123.pdf
Best of luck!