Guy's,
I live in the SFV, SpiderMite Central, so to speak. I have yet to experience them. Proactive measures. Plants from seed. Einstein Oil, Neem Oil, Rooms cleaned after every harvest with bleach and water. Equipment cleaned, maintaining a CLEAN environment. Filters changed or cleaned every week. Not letting another soul except for Jesus to enter grow rooms. Clean change of clothes and booties. It's a pain in the ass but it ensures I have no pests in my grows.
Like I said, Neem Oil or Einstein Oil werks for me in my grows.