This is of the other common problems I occur, Fortunately at the moment it only seems to occur on the Pepper plants and only in one greenhouse (The plastic one, Though I’m not sure why)

I have tried some of the ideas displayed around the internet such as using a solution of water & washing up liquid, Unfortunately not which must success.

The water and milk solution I use on the cucumbers above seems to help slightly.

At the moment though the way I get rid of the whitefly is quite simple albeit a little long winded. I purchased a rechargable low power portable vacuum cleaner normally used for vacuuming cars. Now every week or so I go around the plants with Whitefly and vacuum all the whitefly off the plants.

This is 100% successfully, Although you do have to make sure the vacuum cleaner is low powered otherwise you’ll suck up the plant leaves as well .