My philosophy is to work WITH nature, so here are some options for you to consider:

1. White flies do best where the soil is deficient in phosphorous or magnesium. I don't know if you've had a soil test done,but you could probably guess this is part of the problem. Mineral deficiencies can be easily corrected over time by adding the minerals to the soil. Part of my regular maintenance regime is to add 1 tblpsn of Epsom salts (magnesium sulphate) – which is cheap and easily available from the chemist, produce store or supermarket – to 9L bucket or watering can. Water in monthly. You can also add dolomite (calcium & magnesium), rock phosphate (these are the rock minerals I refer to in the above post which provides a balance of soil minerals) or wood ash (if you have a fireplace) to the soil. i.e. tip the scales in your favour by altering the environment so they won't want to live there!

2. Spray with a certified organic oil based product like Eco-Oil that will suffocate them. Check after 2-3 days and spray again if needed. It's useful to have a product like this in your arsenal.

3. Try growing LOTS of nasturtiums under the plants being affected. (See http://themicrogardener.com/20-reasons-to-gr...)

4. Grow pest-repellent plants in your garden to use in homemade sprays or as companion plants to protect against white flies. Penny Woodward has an excellent book (on my bookshelf) called 'Pest-Repellent Plants' which is worth borrowing from the library. She lists many plants including lavender, basils, calendula, onions, pyrethrum, rosemary,thyme, tomatoes, derris, feverfew, quassia, rhubarb and wormwood that are effective against white fly when used in a variety of ways. I won't list them all here but you may want to pick up some ideas from her helpful book.

5. You can also try making your own yellow sticky traps as a last resort as these also attract beneficial insects. The idea is the flying insects are attracted to the colour and get stuck there. Sticky boards are made from lightweight plywood painted yellow or you can use cardboard (cover in yellow contact or paint to make it weatherproof). Use 6 cm x 15 cm or 30 cm x 30 cm as a size guide depending on the area you have to cover. Spread with glue or spray oil to form a sticky surface. Attach with a paper clip and hang or secure to a stake. Replace traps weekly or when full.Traps should be positioned 60 – 70 cm above the plants to be effective if hanging. Yellow sticky traps can be used for white flies, winged aphids and leaf mining flies too. (See http://www.asktheexterminator.com/Pest%20Con... photo). Hope this helps!