First it is normal for plants to begin dying from the bottom up as they age. Leaves will yellow and them turn brown.

Second, one of the most common of the tomato foliage diseases - Early Blight - causes the lower leaves to yellow and develop brown spots typically called "bulls-eye" or "targets". You can find lots of pictures of EB on the web to compare to your plants.

But the most common cause - by far - of yellowing leaves is over-watering. It causes root rot and nutrient deprivation. I'd need to see a photo of the leaves or have more details on their growing conditions to be more specific. You don't say if they are in the ground or in containers, how often you feed or with what, how often you water, how old the plants are, etc.?

Dave

I've already cut off 2-3 leaves per most plants because they were starting to turn yellow. Part of the cause was some beat down rains that added a lot of dirt to the bottom leaves. But even in the GH, where there were no rains, leaves eventually turned yellow then brown, if I left them on long enough. Personally, if they are not completely contributing to photosynthesis, I see no reason to let them have any food!

Mike

I agree with digidirt from my own experience.

This first pic is of my cherry tomatoe plant whichseems to yellow on one half of the branch some times and other es it yellows towards the bottom of plant Any ideas?

The 1st plant has nutrient problems possibly due to over watering. The 2nd looks like early blight IMO.

I am really interested in this question. Is that last picture dying leaves or is it early blight. I don't see bulls-eye spots. This confuses me. I've had a few of the same.
Karen

Ive had the same........and I want to know if we should trash the whole plant, will it transfer to other plants? what to do? Is it possible to get rid of it somehow? Thanks,
KP

Blight isn't always target shaped. Yes, it can spread to other plants although it may not. Stressed plants are more susceptible. Remove the effected leaves, get a copper fungicide and dust top and bottom of leaves. The earlier you catch it the better. Plants with blight can still produce fruit but usually very little compared to healthy plants. Don't save the seeds from a plant with blight.
Jennifer

Copper fungicides are more dangerous to your health if the right precautions are not taken. I would use Serenade if you want to stay as organic as possible but if you don't care then Daconil should work to control the fungus. Nothing IME will cure the plant but fungicide will slow the progress of the fungus so you can continue to get a decent harvest.

Taz, can you expound on the precautions that need to be taken with copper fungicide? I picked some up a couple weeks ago to spray on a plum tree in the fall, but haven't used it yet.

I think it is early blight. I have the same thing in my garden, where many of the plants have "classic" early blight symptoms, and the other plants have leaves that turn yellow and wilt.

It seems to have a little to due with variety, the exact same thing happened last year, my three chocolate cherry plants never got brown spots (bullseye or otherwise), but the leaves turned yellow and wilted. All the other plants had typical early blight symptoms, and got them pretty bad because I didn't know how to control them.

This year it's under control from fungicide spraying, so the plants are still very healthy (except one of the yellow-leafed wilters, whose symptoms we didn't notice quickly enough to control with spray).

spaghetina read the label and follow it closely. Protective clothing, mask and eye wear are very important. Don't spray if it's windy. Here's a link with the permanent health issues faced when using copper sulfate fungicides.

Here is a link that might be useful: Copper sulfate