OK, she sent me some pix ....

IF it is any of those issues then yes it will likely spread to the rest of the plant. Alternaria being the most likely of the ones you list.

However there are many other things it could be as well - some no problem. Without seeing at least a photo it is impossible to ID what the problem may be. I'd hate to advise using a fungicide on them when it might not even help or if there may be nothing wrong but that is your/her choice.

If posting a picture simply isn't possible then I'd suggest consulting with a local experienced gardener or your local county ag extension office for input.

If a photo is possible then I'd suggest you post it over on the Growing Tomatoes forum here for best results.

Dave

Ahh photo wasn't there when I was posting.

Bad news if I am correct but that is a big IF. That stem looks like early stages of Fusarium Wilt but the only way to know for sure is to wait a bit and see if the plant wilts or to cut the stem open and look for the brown vascular tissue inside.

I'd suggest she Google FW and compare the many images of the disease in the stems to her plant and then decide whether to pull the plant or just keep an eye on it.

"Fusarium fungi survive in the soil or associated with plant debris for up to ten years. Disease development is favored by warm soil temperatures, and symptoms are most prevalent when temperatures range from 80-90 degrees F. The fungi enter the plants through their roots and are then spread throughout the plant by the plant's water-conducting vessels."

Tell her I really hope I am wrong.

Dave

Here's another look. She hasn't done proper crop rotation in her raised bed, and I fear a soil pathogen from a previous year.

To me, there is no BLACK or DARK green color anywhere. It is kind of purple (!?). Could be due to the chemistry of the soil.
JMO

@ Seysonn, the pictures don't really capture the state of the stalks, they ARE very dark, unusually so in my opinion. I'll probably go back up there today & can hopefully get some better shots than she did. Although most of the plants look healthy above the stalks, a few have died off.

Here's one that had no flowers on it that we pulled out to send to the the local UCONN extension to check out.

Don't know how close UCONN ext is to you/her, and what they charge, but state CAES lab has offices in Windsor and the main plant pathology lab in New Haven. They won't charge anything to look at it, you can call to see if pathologist is in the office today and can even get answer on the spot if you bring it in while he/she is there

Here is a link that might be useful: CAES Plant Disease page

As I mentioned above there is a simple test you can do for fusarium - slice open part of the stem lengthwise. Brown pith, sometimes gooey, inside the stem is a definitive diagnosis. Pics of the appearance of the infected pith are available online for comparison if needed.

Dave

I know this post in 2 years old but I seem to be having the same problems with my tomato plants this year. Zap-Man did you find out what it was? All this only appeared in the last few days. The cherry tomato plant in the second picture has died in 48 hours. I have 20 more plants and would like to save what I can. Thanks

Looks like Late Blight to me, the most dreaded tomato disease, based on the rotting fruit with characteristic appearance (upper left) and rapid plant death.

If you have other healthy plants, you can try treating with a heavy treatment of Daconil. Not sure what other options are available to home gardeners.

See http://www.usablight.org

Sorry for your loss :(

I suggest you contact your local extension to report the case and get a confirmation. They do free testing for LB, and can recommend a treatment.