Carol, The best time to prune a magnolia is after it blooms. Pruning a mature magnolia is not recommended as large cuts heal slowly and encourage disease. However, dead or awkward limbs should be removed. I would hire a certified arborist to work on this tree. A product called AzaMax is a broad spectrum pesticide that will kill scale. Check out out on Yardener.com. Best And Happy Yardening, Nancy.