I noticed one mugho pine about two weeks ago fully covered in white specks which are the eggs of the European Sawfly. I first noticed this pest last May when the eggs had already hatched and they had begun to do some damage. This year I checked my plants earlier, in the hopes of catching any infestation at the beginning of their life cycle. I sprayed the infected pine with Safer® Brand 3-in-1 Garden Spray. As of today, nothing appears to have matured and the spots are powdery but still on the needles. As recommended in this article on control methods, I’m going to spray the affected plants quite hard with water tomorrow to see if that will wash off the remaining eggs. I’ll continue to keep a close eye for any that hatch and proceed from there.
Other useful resources:
Ohio State University Extension Fact Sheet