Discolored patches on leaves of young tomato plants.

[Vanisle_BC]

What's this on my tomato leaves?

Its more brownish than the white color that shows on my screen. The plants have been under lights indoors, swapped outside on milder days; had one foliar spray of very dilute Miracle-Gro and been rained on a few times since.

[applestar]

Hey I recognized the damage as something I’d seen before and felt that it’s not serious and seedlings will grow out of it, but couldn’t remember if I’d ever found out what was the cause.

This seems like the right one — what do you think?

Tomato Woes - Texas Plant Disease Diagnostic Lab
https://plantclinic.tamu.edu/2011/05/10/tomato-woes/

The damages are observed as sunken, tan to brown leaf spots.


Tomato seedling leaf exhibiting damage from exposure to cold conditions.
[…]
This damage is consistent with cold damage. In a hard freeze, the entire tomato plant will collapse. However, when it is actively growing and temperature are unusually cold, these symptoms are typically observed.

[pepperhead212]

I got a few like that on tomatoes, as well as my eggplants, because the leaves grew into the lights, briefly. Only relatively cool t8 bulbs, but that was definitely what it was, because it was before putting them out, and it was scattered around, not really that much of it.

[applestar]

Yep, I could see being too close to the lights as culprit too.

Lower seedling leaves get pruned off anyway, but until then, guard against the damaged leaves becoming susceptible to fungal issues by spraying with a preventative.

[Vanisle_BC]

Thanks apple & pepper. In this case I think being too close to the lights is the most likely explanation. I was a bit late in hoisting them up a notch. So far I"m not too worried. The plants are still growing well.