Is this mealybug on my weeping cherry tree?
I think those are apple mealybugs on your cherry tree.
Your best bet for control now is to apply a systemic insecticide which will get into the plant and poison them. Next year in the early spring apply a dormant oil spray to suffocate the overwintering adults. The oil spray should be applied before the buds open and be sure to get good coverage into all the cracks and crevasses on the bark and trunk.