2 Answers

It's a scale infestation. Try to use a natural type of pesticide first before moving on to the hard-core stuff. We have very good success with Ultra-Fine Pesticidal Oil mixed at 3 tablespoons per gallon of water and sprayed on at the first sign of trouble. You can then use an old, soft toothbrush to clean the pests away. Other growers have reported success with Hot Pepper Wax, and lately, Neem Oil. If you decide to go in for the hard-core stuff, any type of pesticide formulated for Ornamentals will work. Go to your nursery and ask them for help. You should not leave any leaves on the ground. Pick them up and destroy them. Do not leave damp places for them to hide in.

I used water mixed with small amounts of dish detergent to spray on the leaves (esp. from underneath).  The white flies disappeared after repeating a few times.