One clarification -- although I said they're "puffy", they aren't really light and airy. They're firm sores. Sorry if that confused the issue.

Folks are likely to say they're root initials. But these are more "puffy" as you say.

What sort of weed killer are you using? Either in the garden or nearby or on the lawn?

I ask because it looks very much what was verified as herbicide damage on the stem of a cabbage. Some herbicides for home use mimic auxins, and the plant parts grow much more than normal-- in other words, in an exaggerated fashion.

I don't use any weed killer in the garden - I try to stay as "organic" as possible. I'm not a huge lawn dude so I hire that job out, and I'm not sure what chemicals are used there. I doubt they would have done any spot-treatment, but probably did a dose of something with a spreader. I do, however, have one jerk-weed neighbor to my south that can't leave nature alone. He's got a huge plot of land with a lot of trees, and he's always out there with chainsaw chopping down the big ones or spraying Round-Up or something to kill the undergrowth.

If it's herbicide damage, it looks like the plants may recover. Any concerns about eating the fruits they bear?

Any other possibilities?

If it's herbicide, it's more likely to be 2,4-D than Roundup.

2,4-D is an herbicide in which mimics natural plant hormone auxins. Here, plant parts grow much more than normal and can look like tumors -- like the "puffy" stuff on your tom's stems.

Whenever Roundup or other herbicides with the active ingredient glyphosate are applied during the growing season, the newest growth takes on a bright yellow to pale yellow coloration.

That said, many weed killers easily move on a breeze, whether via the spray turbulence, alone, or via a mild breeze such as when the leaves are barely rustling.

As it turns out, tomatoes are very sensitive to herbicides.

Just got in touch with my lawn guy. He says that he sprayed some Battleship III (which doesn't appear to have 2,4-D) about 8 weeks ago. Seems too long ago to me, as I had just put the plants in around that time.

Think it could cause something like this?

If the soil has been very moist for a prolonger period, then those "growths" are root nodules. This is not uncommon if the conditions are good because tomatoes are very geotropic.

A picture sure would help! I think that jean001 may be onto something here, indeed if you have a "chemically induced" neighbor. Dicamba is common in many lawn herbicides and there is such a thing as "drift". You might google Dicamba tomato damage, go to images, and you will see a good (copyrighted or I would have posted it) picture of that damage. If it looks different, petzold6596 is likely right.
hortster

These may well be root initials. But they are exaggerated. Thus, the suggestion of weed killer.

The symptoms from dicamba and 2,4-D are very similar. One needs a detailed history to differentiate between the two.

And sometimes you'll never know the source -- drift can move miles when atmospheric conditions are correct.

My tomatoes have the same problem. The following information was forwarded to me by our wonderful local Master Gardeners:

"We are assuming the rest of the plant is doing fine - setting fruit....

It looks like splitting of the stem. You get adventitious roots starting to form in the interior.

Bruising, ruptures, growth of adventitious roots on the stem.

It is not uncommon to see the growth of adventitious roots on the stem. These appear progressively. First numerous small. isolated or aligned protuberances appear. These then split, giving rise to a root which may remain very short (preliminary root) or reach several centimetres. In some cases, the roots appear more suddenly, stems break and the cortical tissues break off.

This phenomenon can occur at all levels of the stem, both near the collar and in the middle (very rare at the top). It is often an indicator of poor 'plant functioning'. In fact, when plants are too vigorous or when their supply of water and nutritional elements is disturbed (in the case of changes to the roots or stem), they often produce adventitious roots. This is particularly the case with attacks of pith necrosis. This bacterial disease attacks the pith and the cortical tissues of the stem. Certain herbicides absorbed by the roots can also lead to the appearance of many preliminary roots on the stem, in addition to the foliar symptoms.

From A Colour Atlas of Tomato Diseases - Observation, Identification and Control by D. Blancard"

mary,

Your Master Gardenrs are partly correct. Yes, looks very much like adventitious roots.

But what you see on OP's stems are larger than adventitious roots. These are overgrown, more tumor-like than normal.

This occurs with exposure to 2,4-D, a component of various weed killers, among them Crossbow and some of the lawn weed-and-feed formulas.

Tomatoes are very sensitive to various herbicides.