Found the reference below while tunneling backward from a recent publication. The latter was a GMO paper showing that a protein from fern, when expressed in cotton, controls white flies and the viruses that they spread. The reference within that paper cited work (shown below) wherein a foliar spray made from an extract or possibly tea from ferns was sufficient to control several damaging insects. I can't get a hold of the full original reference, but if someone was interested in trying such an approach and have access to the ferns indicated (sorry, they used short hand for the genus and species in the abstract) they may wish to purchase the article. As the protein appears to be insecticidal, an extract may also work as a drench for below-ground problems. White flies are rather rare up here in the north, but I've heard they are quite a problem in warmer climes.
“The most important decision we make is whether we believe we live in a friendly or hostile universe.”― Albert Einstein