i use the sticky yellow strips quite effectively.
welcome to goy.

I'd go with the sticky yellow cards too, if you are persistent. Hang the cards as high up as possible and shake the leaves of your plants every time you go in the greenhouse to make the white fly fly upwards on to them.
My wife once worked for as a researcher at Bath University and brought me home a few tomato plants from their greenhouses. As a result we had a plague of white fly which were resistant to every known pesticide!
I tried the biological control (encarseia?) but it couldn't get to grips with the infestation. The yellow cards did a great job and I used to go around the greenhouse crushing every white fly I could find too. It was eliminated by the next season.
Now I am very reluctant to buy in plants from any commercial source, and if I do, I quarantine them in a frame for a couple of weeks to check they didn't have white fly scales which start hatching.
This is the trouble with buying plants, as they appear free of pests but they have eggs or scales hidden under the leaves.

oh i know that only too well.

It all depends what commercial source! I hpoe your not putting us all under the same umbrella!? Ha Ha!!!