You don't have to use chemicals. Use a horticultural-grade oil to mix in water and spray on the undersides of the leaves.
If you get them every year, use it 3 weeks before they're due to re-appear.
You can also use a fine spray of water to knock some down. You want to focus especially on the undersides of the leaves.
kevin

Thanks Kevin. I tried a mixture of olive oil and dish soap with water ( it was all I had ) and it has reduced the swarm but I need to do it again.

And again and again!

White flies reproduce really quick, so you have to spray every couple of days for about two weeks in order to keep dropping the population down.

good air circulation helps, too.

Jim