After a night of "thinking" about this and a very minimal
amount of research, I've come up with a new conjecture.
I'm certainly not an expert on plant diseases but this is
one I've never seen or heard of, so I'm entertaining the
possibility that it isn't even a plant disease.

Because this occurred inside there hasn't been a lot of
exposure to plant pathogens so maybe there is the
possibility of it being something else. I'm thinking along
the line of it being an opportunistic mold of some kind
that just happened to find my tomato plants.

I've looked up "yellow mold" on Google and find a lot
of returns, none of them strictly relevant, but there is
some indication that this could be a variety of
aspergillus mold.

What think you?

A picture would certainly help but it could be nothing more than them being root bound and over-watered. Root bound plants begin to yellow the lower leaves, develop various spots, then die and fall off. Once all the affected foliage is removed and the plants are transplanted they do fine.

Dave

Dave,

I could look and probably will but I doubt they are rootbound.
Been growing them for years like this and it never
happened. They are in one quart containers at 32 days
after putting the seeds in and I expect to see a nice
root system.

Anyway, how would that explain the bright yellow runoff.
Believe me, this stuff looked almost like yellow printer ink.
Other than that, I've had another look and after spraying
and pinching off the really dead stuff, a picture wouldn't
even show much. A few leaves sort of yellow and
some more that look as if they might be starting to be
infected with something. I suppose the fungicide
helped overnight but at this stage a photo would show
them looking almost normal although a bit the worse
for wear.

Nope. Not rootbound. Not overwatered either.
Had a look just in case and neither of these
conditions exists.

OK. This guess is slim since they are inside but if the house is open....maybe. The only time I see yellow wash off the leaves is when the oak pollen is heavy. We have tons of oak trees so it coats the car, truck the plants, the house, the furniture, the deck, etc. It is done down here but is this oak pollen time in your neighborhood?

Otherwise it is just guess work and fungicides I guess. I can't see anything else but molds or fungus possibilities with the info provided. Can you take part of a plant to the extension office to get an opinion?

Sorry I can't help more.

Dave

Dave,

Thanks for your efforts to figure it out. It's so strange that any
guess seems a slim chance. I don't think the oak pollen idea
gets anywhere either but thanks for the try. They are in a
closed basement, fairly dry but not a lot of air circulation
though nominally air conditioned. We have a lot of oaks
but no sign of pollen anywhere else.

Actually it looks almost like what I would think powdery
mildew would look like, though I've never seen that either.
Except that this is bright yellow.

Just had another look and they seem to be improving a
bit. That's a really fast reaction for a plant in my opinion
but I guess I have to believe my lying eyes. So I suppose
I'll try another application of fungicide later today and
hope for the best.

So sad, these weren't even plants that I intended to keep!
I was going to give them away to people who are eagerly
waiting for them. Not so sure anymore.

Look anything like this?

Hard to believe it indoors but I suppose a basement could harbour it if inadequate circulation.

Still investigating.

Dave

We need pictures!

A picture with a short description can speak volumes, me thinks.

Dave,

Yes, some of it does. Other leaves turned uniformly dark
yellow. And overnight. The day before they looked
perfectly healthy, then overnight - bright yellow orange.
I have no pictures of this because I treated with fungicide
right away and stripped off the most affected leaves.

Also, I think significant the fact that I had another shelf of
plants three feet below these ones that appeared to be
unaffected. One day later though I see the first signs of
the same thing. They have gotten "fungicided" this
morning.

Then of course there is the "yellow printer ink" running off.

Maybe it will never be identified but I will probably know
the end result pretty soon. The fungicide - copper soap
and spreader-sticker seems to be helping.

Thanks again for all your help.

Here's my latest scenario;

1) I think it's pretty definitely a fungus. Which one is uncertain
but according to Dave's reference it could be powdery
mildew or something similar.

2) The indoor location is unusual for that but not impossible.
The area is a back basement. It is not wet and there have
been no other occurrences of mold or mildew. That doesn't
mean it can't happen, especially with the enticing object of
tomato plants, soil and water in a confined area.

3) There is a duct with a register nearby but not very well
located. Consequently, with respect to air circulation,
it is a bit of a dead end. Add moisture and a steady
temperature in the low 70s and it looks as if I may have
created the ideal incubator for some sort of mildew organism.

4) I have used some external soil in there for repotting and
so on. As well, I have entered the area several times a day,
sometimes after working outside in the garden. So, spores
could have come in on clothing or skin.

5) The original occurrence was confined to a single shelf
with an area about 2' by 4'. a dozen plants there might
make an ideal breeding ground for a mildew.

6) The confined area and minimal circulation would have
allowed for a normal pathogen life cycle followed by a
sudden "bloom" of infection and spores. this could account
for the extreme and sudden (overnight) yellowing (oranging)
(sic.) of some leaves while a few others have a more
characterisitc appearance of infection.