Mites is spiders. Anything that will kill spiders and ants will kill people, so we have to be careful not to kill ourselves or our children, pets, et al. All kinds of spiders travel on single strands of silk that they let out and when it gets hung up on something downwind they repel to the new location. If a plant gets overpopulated, they bail out and go to new homes. In a pinch they can just spin a thread and when it can carry their weight, ride the winds until they land on something. All this is important because mites come from someplace else and find their way our plants even after we clean them up with nice poisons. It is important to look around your own area, especially upwind, for a source of new contamination. One of the most notorious mite hotels are large Alberta Spruce, but any dense shrubs that stay dry on the interior can be a source that can constantly re-supply our plants. Look around. If you have a constant problem, there's probably a source nearby, and it probably looks sick. If it belongs to a neighbor, you may have to re-think your practices.