Sounds like whitefly, a very common hibiscus pest.

The miracle chemical to get rid of whiteflies is a systemic called imidacloprid. You can buy it in Bayer Rose and Flower spray or Bayer Tree and Shrub drench. The spray is good for smaller plants, the drench for larger shrub sized plants. Both of these are only labelled for outdoor use, however, and I can't spray outdoors in the winter, obviously. I used to wait until a relatively warm day, drag the plants down a flight of stairs to the garage, line the floor with newspapers, spray and let them dry, then drag them back upstairs. A real nuisance and rarely would we get a suitably warm day when I needed one.

The drench lasts for a year, so theoretically you could treat outdoors in the summer and be good for a year, but that won't help you NOW.

I finally bought a jug of marathon granules, which also contain the same chemical. Unfortunately, the granules are geared towards commercial growers and the smallest size I could find was a jug of 4 or 5 pounds, which costs around $130! I have a lot of plants, so I'll use it up eventually. We also use the granules in my job taking care of office plants - they work very well on fungus gnats, scale, mealybugs, thrips, pretty much any sucking insect EXCEPT spider mites, and we don't have to worry about spraying inside the offices.

Your best bet now would be to spray thoroughly with a horticultural oil, repeat every week for several weeks, and hope that does the trick until you can get the plant outside to use some form of the imidacloprid on it. (I see that you are in Canada - I hope the stuff is available there!)

My first winter with a lot of hibiscus I had spider mites and root rot. The second year I had horrid whiteflies. The third year I used the granues in March (that was March of 2006) and also used a horticultural oil for quick knockdown (the systemic takes a while to work its way into the plant, especially the woodier ones). I have not seen any whiteflies indoors since March of 2006 and I haven't re-treated yet. Some people claim that using imidacloprid can make plants more susceptible to spider mites, but I haven't found that in my experience.

Good luck, and let me know how things work out!

Watergal, thank you so much for your diagnosis and detailed instructions for treatment. Most of the Bayer plant products are restricted for use by homeowners here in Canada, so I'll probably have to go the horticultural oil route. It doesn't seem to be hurting the plant, so I guess waiting until spring will be O.K. Will keep you posted.
Northerner.

You're welcome! I do interior landscaping, and my colleagues in Canada have told me that they basically can't use any chemicals any more.

The whiteflies will eventually hurt the plant when they build up to significant numbers and suck the sap out of the plant, so the sooner you can get it done, the better.

Your point is well taken, Watergal. I'll be off in search of the chemicals this weekend.