Hi Al –
I’ve had great success with both Azamax and Organocide Spray for whiteflies. Azamax comes in a concentrate form which you add to a spray bottle. Organocide comes in a 24oz Ready-To-Use spray bottle. By themselves they are very effective for whiteflies.
For incredibly difficult infestations, I’ve found a weekly rotation of the two plus a pyretherin based insecticide (Azamax wk 1, Organocide wk 2, and Pyretherin wk 3…) seems to decimate just about any insect problem you may have.
Find them here:
https://www.planetnatural.com/product/organocide/
https://www.planetnatural.com/product/azamax-azadirachtin/
https://www.planetnatural.com/product/dont-bug-me-insect-spray/
Good luck!