Don't know why you have such a high pH if in Mel's mix. Perhaps the pH meter is off?

Investigate the soil -- Put a trowel in it. How moist or dry is it? Adjust watering accordingly.

And have you added any fertilizer? If not, do so.

If you have a local cooperative extension bring soil there for testing.

Most likely, the probe is inaccurate (they tend to be inaccurate). Peat moss alone has a pH of 4.5, and none of the other ingredients have a high pH. I don't know what's in Mel's Mix, but it's probably nothing that would cause pH to go up.

I'm going to assume you're not adding baking soda to the soil on a regular basis. :-)

So let's rule out the soil pH for now. Most yellowing in tomato plants is caused by soggy soil and/or overwatering or a lack of nutrients.

Do not water until the soil is dry a few inches down. Stick your finger down into the soil about 3 inches. If it's dry or almost dry, water; if it's still damp, don't water.

Could the roots be sitting in wet, poorly-drained soil? I know it gets pretty warm and dry where you are and you need to water plants more often. Just make sure they aren't sitting in a pool of water and that the soil drains well and can dry out between waterings.

Next: fertilizer. How often are they fertilized and what kind of fertilizer is used?

The photo of the leaf does not look like disease, but it's difficult to tell off a photo of just one leaf. Photos of other leaves and a "full body shot" of the plant would be more instructive. Are there any strange spots or leaf curling on any of the leaves?

I am pretty sure I am not over watering them. I have only watered about 1-2x a week and the temps here have been 75-95 or so the past couple of weeks. It keeps going up and down. Before I water, I Usually will dig down a couple inches into the soil to see what it looks like since the top almost always looks dry a day or 2 after watering. It has never been water logged or soggy. It drains really well. I also added mulch a couple weeks ago just a light layer of pine needles(this problem had already started) I also added shade cloth @ about the same time.

I did fertilize them about a month ago or maybe 6 weeks now with BioFlora� Dry Crumbles 6-6-5. At first I thought maybe I over fertilized, but I would think all plants would have shown signs.. .

The leaves and branches are drying up and shriveling until they fall off or I cut them off. Its going from the bottom of the plant to the top.. .

I did water one raised bed with some vinegar water and those plants seem to be doing well. Our water here has a very high ph.

Nope no baking soda has been added:)

Could be lack of nutrients, I bought a pre packaged mels mix from gro-well here in phoenix. Some of my cucumbers are looking a little yellowish and I was wondering if I should fertilize it or not to help it along.. . Just wasn't sure what was going on with the toms and didn't want to mess them up more!

I stayed up late last night trying to figure it out and came across some info on russet mites... I thought maybe that could be it so I took clippings today and looked at them under my nephews microscope... nothing.. It's just confusing me because it doesn't look like anything I can find online.

There aren't strange spots The only curling has been when it's drying up.

I posted some more pics on my blog

http://duhhworld.blogspot.com/2011/05/here-are-some-more-pics-of-plants.html

http://duhhworld.blogspot.com/2011/05/trying-to-post-pic-that-can-be-enlarged.html

Any help is appreciated! I'm going to be gone for a couple days and will feel bad if they all die while my husband is taking care of them!

Here is a link that might be useful: new pic

I see no sign of leaf disease, no sign of herbicide damage. Looks like this is spreading at a pretty good pace.

I'm sorry to say that I think it might be one of the wilting diseases - either fusarium or verticillium. It doesn't matter which one as there's nothing that can be done for them.

Please get a second opinion, as I've never seen either of those diseases in person; only in other threads and other places on the web.

Please check the link below. Plus, you can Google these diseases and read more about them.

Sigh. I hope that's not the problem, but it really does look like it.

Here is a link that might be useful: Fusarium and Verticillium Wilt Info

According to the University of Arizona, both fusarium and verticillium diseases are uncommon in your area [link below]. You may want to check out the tomato russet mite.

It doesn't look like mite damage to me, but you are in a very different climate/environment with very different pests. Again, I hope someone else chimes in. You've got nothing to lose and might as well get some sulphur to treat for the tomato russet mites.

Hoping for the best.

Here is a link that might be useful: U of AZ

Looked at one of the worst plants today and it has new leaves sprouting toward the bottom of the plant that look beautiful and normal... I had watered this one with a vinegar solution. I checked out the wilts and it just doesn't seem to fit. thanks for all the thoughts! I'll keep looking and get stuff checked out