How old are the plants? This late in the season it is quite normal for plants to begin dying from the bottom up. Have you been harvesting from them all summer? Just remove the dead branches and the plants, if they are indeterminate varieties, may continue to show new growth and the fruit will continue to ripen.

It is impossible to diagnose a disease process without seeing a picture or without very specific details - there are just too many tomato diseases - viruses, molds, bacteria, etc. Yellowing of leaves can be anything from too much water to late blight or more. The link below provides a number of pictures of tomato diseases that may help you define the problem. Also, on the Tomato Pest & Diseases forum there is a thread called Problem Solver 2 with links to many more pictures and info.

Lastly, your local county AG extension office can advise you on what diseases processes are prevalent in your area.

Good luck.

Dave

Here is a link that might be useful: Texas A&M Tomato Disorders

"My tomatoes have some of the bottom branches turning brown/yellow and dying. These are Homestead variety, my favorite. Is this common/natural? is it a fungus? can I do anything? The plants are full of beautiful green tomoatoes ready to turn red. They are in a raised bed with good soil and plenty of water." [Alan]

Alan,

Most of the Homestead selections are determinate, so you may be near the end of new fruit production depending on how much fruit set you've got at this time. And with daylight hours shortening, you might not have time to ripen any future new blossom sets this late in October even though you are far south and a mild winter is predicted. But then you may like fried green tomatoes and chow chow, so while topping the vines might force earlier ripening of the full sized green tomatoes now on the vine, I'm not necessarily advocating topping your vines ... just saying your full term production may be limited this late.

If your bottom leaves are yellowing evenly ... like fading from dark green to a lighter green and then fully yellowing without black spots, dark brown blotches, bullseye rings, or other definite signs of fungal disease, it may simply be a nitrogen deficiency. Nitrogen is mobile in the plant, and when the top shoots growth require nitrogen for cell division and new growth, and insufficient nitrogen is availabe via the roots, the plant will rob N from the older leaves first and transfer it to the new growth.

Did you side dress your plants with a high nitrogen fertilizer after they set green fruit? If not, a good boost of a liquid high nitrogen fertilizer, or a band application of high nitrogen fast release around the plant in the root zone then watered in, might stop the yellowing of lower leaves.

If indeed it is a fungal disease, and you can identify it either by looking at photographs of several Websites specific to tomato desease diagnosis, or you can take some leaves in to your county extension agent and ask her or him to identify the disease, then there are a few steps you can take to contain the fungal disease.

1. Do not move among your plants when they are wet with dew or rain drops as that will rapidly spread the fungal spores.

2. When the plants are dry, slowly snip or pinch off all diseased foliage and dispose of it by bagging or burning it. Dip your snipping tool in a solution of one part Clorox and ten parts water as you move from plant to plant to minimize transmission of the fungal spores.

3. Do not overhead water or splash irrigation water up on the foliage as dry fungal spores lodged on the plants need water to hydrate and become "live" and enter the interior cells of the leaves where they destroy the structure.

These steps may buy you time until your green tomatoes ripen, but if you indeed have time to extend fruit production, you may wish to use a fungicide. If so, first identify whether it is a fungal disorder as you're just wasting your time and money applying fungicide if it is something other than fungal disease.

Click this link and look at the photos of FUNGAL DISEASES

After looking at those photos, if you have doubts, call your Alabama County Extension Agent or the Alabama Master Gardeners Help Hotline for advice and diagnosis.

I'm hoping it's just a nitrogen deficiency that's yellowing your older foliage. That will be easy to fix with organic nitrogen or quick release chemical N.

Bill