I found this info. online, and it's the method I use, too:

Easy way to get rid of white flies

White flies, I hate the things. They get in your food, your drinks, your eyes; you sometimes even breathe them in. In the summer my shrubbery is the white fly Hilton. White flies also known as gnats breed worse than roaches and can infest a home in a matter of days.

I quit having indoor house plants because of white flies. Its bad enough trying to keep the things out of the kitchen garbage.

I tried everything to get rid of them. I used powders, expensive sprays, and those sticky pest strips that you try to hang somewhere so they don't get stuck to your walls and clothes. I found a great way to get rid of them and wanted to pass it on to all you folks who suffer from the little buggers.

Getting rid of white flies is easy. All you need to do is mix a tablespoon of Dawn liquid dishwashing detergent in one gallon of water and spray it on any infected area. Use a hose sprayer, a garden sprayer, or even one of those hand held spray bottles.

Apply it 2-3 times a week for a couple of weeks and your white fly problems will be gone. Soap kills white flies and it won't hurt your plants or the soil or your fruits and vegetables. Spray it on shrubs, fruit trees, house plants, and garbage cans. I can't believe after using all those poisonous pesticides that plain old soap was the best and only thing that has ever worked for me.

This stuff also works great on fruit flies and is just the thing to put on orchards. Its sort of fitting that soap kills white flies considering where they land sometimes.

I use soap also and it really works if you spray many times. Just be careful that it's not too hot, as you might burn the leaves.
the black stuff is ant poop as they eat the whitefly eggs as well as the insects themselves. It might eventually wash off or you can try hosing the leaves clean. It might just be easier to cut the plant back - I have three powderpuffs and find they fill out nicely if cut back, even though you sacrifice blooms.
If you want to prevent whiteflies, Bayer makes a systemic granular which I am trying for the first time this year as I have whiteflies in my gingers and some ground cover. We'll see if it makes a difference next year!
Good luck, they are horrible pests
Hester

Thanks for the suggestions. Today right after dark before
reading your suggestions, I used a mixture of a little
lemon dish soap, vegetable oil and almost a full spray
bottle of water. I think that tomorrow I'll instead
try the dawn soap method and use it 2-3 times a week
for 2 weeks and see what happens, i'll also cut back the
plant a bit too because most of the leaves look blackish
right now. If It still doesn't look too good, I'll probably buy the systemic granular also.
thanks again
Mike