Whitefly nymphs live in the soil, so if what you have is on the plants you have something other than whitefly. If the products you have used did not control these you are in real trouble since all of them are very broad spectrum poisons that will kill everything, including the beneficials that could help control these pests, in your garden.

Whitefly nymphs do NOT live in the soil, but can be found on the underside of the leaves.

I'd suggest that you make sure that the neem oil you are using is cold pressed, which will have a high percentage of the active ingredient Azadirachtin. Be sure to concentrate your spraying activities to the underside of the leaves, where whitefly of all stages hang out.

Azadirachtin has no broad spectrum effect on other insects once it has dried, but will continue to work on those pests that continue to feed on the plant. Since it works as a growth disruptor, the nymphs should never reach adulthood. It also acts as an anti-feedant. Yay!

rhizo: It doesn't say on the container if it's cold pressed or not. It's made no difference in the number of whiteflies. Are they selling products mfged that don't work? We know to spray under the leaves but in a huge garden it's just not possible to get under every leaf. I've been gardening for many years and never saw anything like this infestation before.

There are Neem products on the market that are manufactured by methods that eliminate much of the Azadirachtin from final product. If your container doesn't say that it's cold pressed and give the actual percentage of this active ingredient on it, then it's not cold pressed. Remember, Azadirachtin works as an anti-feedant and growth regulator for plant feeding pests.

Please know that the use of highly toxic broad spectrum pesticides such as malathion, Sevin, Bug-B-Gone (yikes), etc. have been proven to cause a dramatic reactive resurgence of pest insect populations.