My name is Tom Holmes
I have been growing vegetables since I was 14 years old, I now draw social security so it has been a long time.
I live just south of San Francisco in climate zone 10A. We only get frost about once every 3 years for about 3 days.
I mainly plant tomatoes, lots of them, like 54 plants, about 25 varieties (I have cut down due to the drought). I plant them in large containers with the bottom of the plastic containers cut off and I use wire mesh on the bottom of the container to keep gophers out. I put them in raised beds and use Texas Tomato cages for support. I have recently got into planting lettuce and plan to do some strawberries.
This year I had a cold frame built (I do many things poorly, carpentry is one of the things I do poorly). I was able to utilize some old shower doors for the glass. I am expecting great things from it.
The last 7 years I have had to fight white flies and aphids. I may have a crop rotation issue. I compost grass clippings, leaves and straw during the year. I add some steer manure and mix it into my beds.
Interested if any one has success in stopping white flies before they hatch.
When you mentioned white flies and California, I immediately thought about those darn citrus trees/ plants that they live so much. You have quite a number of tomato plants going. Awesome. If the problem is not too bad, you could always carefully hand pick the leaves that have white flies/ eggs on them and toss them in a garbage bag. I would immediately tie the bag up after doing so. Again, that's if the problem is not too bad. For more of a prevention; try using placing aluminum foil on top of the soil or using a reflective mulch. This will actually deter them. Praying Mantis is also a good natural method to getting rid of a good number of those unwanted bugs in your garden, including white flies. Lady bugs are another good choice, but they may not do anything for your white fly problem as they only eat a particular species.
I hope the information was helpful. Let me know of the methods you decide and keep us posted.