Hi Naysen,
Your disease problems sure sound discouraging. I don't know enough about such things to venture an opinion on what to do (seems like you've tried about everything), but you might go to the following link, and then click on the appropriate links to get to your country extension contacts. (I didn't link directly to this as I though you might find some of the intevening info of interest).
http://www.wrpmc.ucdavis.edu/
When you get to the county extension info part of it says:
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University Extension in my State
Extension services vary by state and county. Local knowledge can often be the best resource for your specific questions. You will need to check with your local Extension office to determine what expertise is in your area, but traditional services that Extension may provide include:
- Pest identification and/or plant disease diagnostic services
- Pest control recommendations
- Soil testing to determine fertilizer needs
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I'd give them a call. I'm guessing that their services are probably free or very inexpensive and they could probably solve your problem pretty quickly or maybe refer you to someone at Davis who could. I think that since the tomato industry is so important to the central valley, they really are interested in finding out what sort of problems home gardeners are having so they can pin point outbreaks of things to alert the industry if necessary.
Good Luck!
Anne