Here's info from Univ CA
http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7400.html

Here is a link that might be useful: giant whiteflies

I finally cut mine to the ground. They are re-growing and I am keeping on top of those %!!@ whiteflies.

When all else failed for eradicating them on one particular hibiscus plant, I sprayed it with a light oil spray with fixed copper. It worked, and to my surprise, did not damage any of the foliage. That was a year ago. They have returned, so I'm ready to try the same treatment again.

For whitefly on hibiscus is you need to treat the plant with both insecticide (for the tiny white flies) and fungicide (for the hairy white stuff). Some people spray the bushes with sulfur, but I find that doesn't seem to be enough, and in any case the plant should not be sprayed with something else before the sulfur spray because then the spray will just rinse it off. It also takes a lot of spray to fully get all the leaves in a big hibiscus bush, which makes me reluctant to use Daconil, since I really do not want to be spraying that much of an environmentally unfriendly, slightly toxic, chemical in the yard.