Hey Rob927,
You should buy some CannaCure, in my opinion one of the best stuff arround.
It kills all kinds of insects and plagues like mildew.
In your case it does kill Whiteflies as well.
What awesome about CannaCure is that it is environmentally friendly, so it is organic, it is doesn't have toxic stuff in it.
i can be sprayed on your plants in every stage! So even with buds on your plant.
If you have heavly infected you should spray every 3-4 days, if you have a minor infection or just like to prefend, once a week.
It is also a awesome leaf feeder.
Good luck killing those flies and growing your plant(s) :)