If your mugo pine looks as though it has been spattered with white paint, it's likely it has pine needle scale. Adults are difficult to control, but the crawler stage (young, recently hatched scales) is easy to control with insecticidal soap or horticultural oil. Eggs hatch in midspring, about the time that white bridalwreath spirea blooms. Watch for the crawlers, and spray to thoroughly cover needles and stems. 

Answered by BHGgardenEditors