Unfortunately I have spider mites on some of my plants. I spray with safer's insecticidal soap. I already use it on two of my plants, but I just wanted to verify that it won't hurt my orchids or their roots if I use it over a long period of time.
It wont hurt your plants. Sometimes roots can be a bit sensitive, but generally not too much. Many orchid growers use it. Just be watchful of direct sun hitting a plant that has been sprayed, especially if its still wet. It will intensify the effect of the sun.
You'll need to retreat the plants after a week or 2, and at least 2 more times. If the infestations are severe, repotting after first treatment can help.