Whiteflies already

I have an infestation of white flies on my two live oak trees (the trees are growing in a heavily mulched area, not in the lawn). It is only February for goodness sake. The flies have been there about a week. The trees are about 10-15 feet tall. Can't imagine trying to spray something that tall. Should I be worried? I am guessing they will be moving into other parts of the garden soon.