Did you by chance put them outside on a nice warm sunny day at any point?

The leaves in first pic look sunburned to me... in the other pics I'd suspect nutrient deficiency.

I agree, some kind of sunburn or light burn. Are the leaves crunchy?

Leaves are not crunch, but the texture has changed a bit. Yes I did keep all seedlings for an hour or two outside on sunny day. Also the light bulb is close to the one that has white leaf. How to fix this ?

Is it ok to still keep others on south facing window ?

If the yellow ones are nutrient deficiency then I can feed them

Looks like sun burn. Either too close to the light source or damaged from the sun. Just don't let them exposed to too much direct heat.

Yup, sun or wind burn, even if it was only for that one hour.

Yeah, it doesn't take long for them to burn in direct sunlight, if you wanna harden them off, do it gradually in the shady part of your yard. As far as the light, the 120w Phillips sounds like an incandescent light, which can put off lots of heat, I would use just leds or fluorescent bulbs

Another vote for sun burn blotches.

I usually keep mine in the shade first day. I give them early morning sun a bit first and keep increasing the duration. That is what hardening off is about. Also never put then in the sun with wet leaves. .

sey

We can politely agree to disagree about wet leaves causing damage in the sun. I grew at a wholesale nursery in Houston Texas and we overhead irrigated every day in that dang hot sun. Never, did we see evidence of sunburn.

yeah that is a myth about the sun burning leaves if they are wet. i worked for a golf course for many years and we watered like crazy in full sun 90+ degrees.
but it is not recommended for other reasons (evaporation, plant water uptake, etc)..

there is however a thing called wind burn.

Wind + sun + cool temps is a formula for bad leaf burn. Your plants will recover if you're more careful and gradual about hardening off.

I've had that happen and plants react to burn in different colors, I've seen white, silver, and a copper brown. As everyone stated harden them off to outdoor conditions and they will be fine. Your plants were not badly burned they will be fine.

Just wanted to share an update. I had 20+ seedlings, initial burn started with just 2-3 of them, now it has pretty much spread to all seedlings. I still have them all indoors on south facing window. It seems like either they are still getting burnt with direct sunlight coming from south facing window OR they caught some disease. Here are the new pics. There is some white scaling on the stem, and almost all of the leaves are curling-up and after few days they fall off even with light touch.

- I re-potted at least 10 of them with new soil just in case if it's in the soil and also just in case if I had over watered them, wanted to take-out that moisture and start fresh again.

Any solutions ?

@ in each cup is over-crowding for one thing, especially that size plant. Why are they doubled up like that but we need a much closer photo of the white stuff on the stems to tell what it is. Are you sure you don't have an insect pest issue going on? Look very closely.

Dave

Sure looks like herbicide injury. Roundup drift somehow may have caused initial damage but the curling is more typical of 2-4D injury. So I guess I'm indicating that I'm confused by what you pictured.

You might need to investigate the source. Compost from lawn clippings is often suspect. What about the potting mix? You did what you could to transplant but often plants are slow to recover from this type setback. Only time will tell.

@digdirt2 :

They are big cups. I started 2 seeds in one container from early on, didn't wanted to disturb their roots by separating so I kept many of these as is. I have few that I separated to take risk. They all have the safe fate irrespective.

I have 3 types of basil, pepper and cucumber within few inches away from these tomato plants, all others are thriving. Other than some flies there are no pests I can see. I used some organic fertilizer that might be source of the flies. It's possible that, whatever this is affecting only tomatoes.

@Barrie: I am new to gardening, so I didn't understand any of first paragraph. There is no lawn clippings or any kind of pesticides I have used.

backyardigan: I used some organic fertilizer that might be source of the flies.

How much did you use? And when? All of those symptoms could be from overfertilizing.

I used half strength as quoted on the packaging. Fertilizer I used is "Espoma Organic Start" which 1-2-2.

Originally I reported some sunburn in this thread and I also saw lot of yellow leaves, so I fertilized. But at the same time I had moved seedlings from just artificial lights to sunlight. This wilting started just couple days after fertilizing, so you may be right.

Is there any way to correct it ?

What Barrie is saying is the top growth on the plants looks like they have been exposed to herbicides - weed killers. I assumed they have never been outdoors where they could have been exposed to it but if there is any in a garage and if they are located nearby they can be exposed that way.

It sounds as if you have an infestation of fungus gnats - the flies - but it is all the larvae in the soil that really do the damage. For every fly you see there are 50 larvae. 95% of the time they are do to over-watering, soil kept overly wet. They can be killed by buying some Mosquito Dunks and dissolving one of them in the water you use to water them. You also need to let them dry out more between waterings.

"They are big cups. I started 2 seeds in one container from early on, didn't wanted to disturb their roots by separating so I kept many of these as is. I have few that I separated to take risk. They all have the safe fate irrespective."

I understand what you are saying but those cups are intended for 1 plant only. The two are competing with each other for root space, nutrients, and water. It is probably far too late to separate them now without killing one of them anyway so the best bet is to sacrifice one by cutting it off to save the other one.

I suspect you also have either aphids or scale growing on the stems which is why I asked for a closer pic of the white stem.

And like gorbelly said - fertilizer root burn is also possible. At this age no more than 1/2 strength fertilizer is recommended and 1/4 strength is even better. But organic fertilizers like the Espoma, while great for the garden, are not good for small containers. There is no soil bacteria in the mix to digest them so the plants can use the nutrients. Liquid, pre-digested of water soluble fertilizers work far better.

Dave

i can see some bugs on the plants, you must have serious gnat problem. while they normally won't kill a plant, if you have a lot of larvae in the soil (where they form) then they will basically devour the roots of the plants. normally, they feed off fungus, but once the supply of fungus is gone, they will eat away at the roots.. on a large healthy plant this is usually rare as the plant is big enough to have a adequate root system to sustain the plant, but on a small young plant, not so much.

you can use neem oil as a soil drench to kill the larvae in the soil, but you will have to apply it to all your plants in the house as they're also likely infected with larvae.

Here is the close-up.

BTW. The small black stuff you see around on some plant stems are not gnats, it's just some potting soil that touched the leaves. I do see few gnats here and there but not a lot.

Last week before this white stuff developed, when I touch the stem it used to be wet with some oily stuff on it which smelled of typical tomato plants.

So these plants have been outside?

If so that makes a lot of difference in what they have been exposed to. This latest stem photo looks like it might be mites but it could also be one of the fungus blights if the plants have been outside. Mites can be treated and recover if they haven't done too much damage. Fungus infection is a whole other ballgame.

Either way I tend to agree with gorbelly, start new plants as these may not be salvageable.

Dave

And next time do not put them outside until they're ready to be outside permanently. plants do not like to be Yo-Yo'd around.. either keep outside or inside. putting them outside for a day, even for just an hour or two, just because it's nice and warm to you, does not help them at all.. IN OR OUT, can't stress that enough.

while putting them outside likely did not rot the stem, it weaken/stressed the plants most likely from wind burn, especially if they were grown without the present of artificial wind (ie a fan). personally, i always have a slight breeze on my plants from an oscillating fan when growing indoors.. not only that, but you end up with a much stronger plant from the movement. once they go out they're more used to it.

Just an update:

Even after replanting and putting inside house with grow lights, my seedlings were looking terrible, almost rotten to death. So I gave-up and decided to keep them out of the house under shade. May be the change in weather (it's sunny) or just open air, 90% of them have revived, they are looking much better than before. They are ready to be transplanted again to their final growing space.

Funny thing is, I just too many now, because I started some back-up seedlings too, they are thriving well :)

Thanks for all your help.

Learning here is to have patience, be gentle with seedlings and be prepared for the worse.

Seedlings that have had way too much attention paid to them and too many interventions performed on them can start to magically recover after people give up on them and "neglect" them.

Too many seedlings is never a problem. Keep some of them, as you never know when you might need to replace a plant. As for the rest, you can always give them away.