I use a systemic granule mixed into the soil every 6 weeks. If I still see whiteflies, I also will hit it with Safer (I use the concentrate & mix it). When they go outside, I use the yellow sticky traps, too. I have tried the "natrual way" with insecidal soap to no avail. This will be the 1st year I'm using the systemic on a regular basis - have it marked on my calender! I, too, have lost several hibiscus & a rose tree to these nasty things.

I'm betting that a solution of Sevin poured into the soil would kill off just about anything that is living there. It isn't labeled for inside use, however, so it would have to wait until they go outside to use it.

My son-in-law had problems with the white flies on his hibiscus indoors and he covered the soil with press and seal (the stuff for sealing bowls etc. with food in fridge) completely covering it from plant to edges of planter so it's good and sealed in. Then he took all his leaves off the plant and left it that way till he was sure all the eggs in the soil had died (this is where the eggs are layed and hatched). Then he uncovered it and started watering it again. It looks beautiful now. Be sure you don't have white flies on other house plants though.

First, make sure your watering is under control. A plant's best defense against insects and disease is a robust metabolism. Something else to watch out for is root congestion. Root congestion slows extension, causes loss of interior foliage so most growth is concentrated near apices (growing tips of branches) and causes buds to abort. Make sure you're using a fertilizer LOW in P and heavy on K. I use Foliage-Pro 9-3-6, fortified with a little Pro-TeKt 0-0-3, which also helps to harden cells against infection and insect predation.

That said, if you want an effective insecticide with residual protection, I would suggest Bayer Advanced 3-in-1 Insect, Disease, and Mite Control. The insecticide (imidicloprid) and the fungicide (tebuconazole) both act systemically. These chemicals are approved for houseplants, but shouldn't be sprayed indoors.

Alternately, you can purchase a liquid soil drench containing a 1.5% solution of imidicloprid and mix it at 1 tsp/qt of water, and use it to drench the soil. The shrub will take the insecticide up through the soil and kill insects that feed on sap, and any insects in the soil will be killed.I don't like the granular vehicles that carry imidacloprid (Merit/Marathon/Dragon ....) because they filter down into the soil, and I've repeatedly seen evidence of weakened root systems (often severe) whenever I've used them.

Imidicloprid does impact some pollinators - especially bees, so keep that in mind in deciding if imidicloprid is a good choice for you. I use it almost exclusively on my bonsai trees, and only the blooming trees hold any interest for pollinators, so I avoid using it during the bloom cycle.

Al