It sounds like you've mealy bugs. First, isolate the infected plants away from all other plants. Keep an eye on the plants that were close to the infected plants, if any get mealy bugs they are easier to cure. The Cure: if it is a small colony, you can remove them with Q-tips dipped in alcohol. If it is a larger infestation, you will have to spray them with an insecticide made for mealy bugs. You will probably have to spray two times at an 8 day interval.(what ever the bottle instructions say) Or go with a systemic chemical for whole plant coverage. If you go with the chemicals, READ the label first, before starting anything.