we use a product called natural pyrethrum when we need to, not sure what's in it but must check now, wouldn't have imagined it had petroleum in it as the natural product is supposed to be made from daisy's

len

Here is a link that might be useful: lens garden page

Insecticides, pyrethrins, have very limited affect on the Whitefly killing off more of the beneficials that could help than the target. Insecticidal soaps and Neem Oil products seem to have better control of nymphs, when sprayed directly on them, then anything.

Here is a link that might be useful: About Whiteflies

thanks kimmsr, I had read the same warning about neem, so I think I'll stick with soap spray. Mine has not been effective so far, but I only added vegetable oil to the mixture yesterday, so I hope that is the key.