Answer: Whitefly is very difficult to eradicate once there is a large established population on indoor plants. Sometimes you will need to isolate the infested plants and possibly get rid of the worst infested ones to try to reduce the numbers. Then you can spray with either insecticidal soap or horticultural oil (not both at once) to try to control them. Read the label to be sure the product can be used on the plant you intend to spray and carefully follow the label instructions. You need to spray every surface of the plant and you may need to follow up to control subsequent generations. In the fall, in my experience it helped to wash all of the plants thoroughly with a spray of water and then during the week or two that I set them in the shade prior to bringing them inside (to acclimate them to the lower light) I would also inspect them very carefully. If I saw any pests I would either spray with soap or oil, or discard the plant rather than introduce a so called "whitefly magnet" indoors. I hope this helps.
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