It was a starter plant (about 5 inches tall), already out in the weather at the garden center. Haven't noticed the temps each night, but it may have been below 50 once recently.

Could also be blight. Are the upper leaves looking better than the lower leaves? Fungal infection would mainly be on lower leaves. Sun damage would largely be on the less shaded upper leaves.

Attached pix - on lower leafs on this plant, on upper on another, although no shade on the lower ones that have the disease.

PS - this forum is amazing - just joined two hours ago, posted my first time, and responses already! Wow!!

Well, that one picture looks like a fungus infection. Lower leaves mainly affected. The fungus lives in the soil, and splashes or blows onto lower leaves. More common if humidity is high, or if there has been a lot of rain. If that's what's going on, you can give up on the affected leaves, and might be smart to remove them. For the unaffected leaves, fungicide is in order. This is a VERY common problem. Was commercial potting soil used in those containers? That's usually sterile, and fungal infections are less likely.

Dan - thanks again. Will trim off leaves and try fungicide. No potting soil used, have these new plants in pots used in prior year, and have added compost and fish emulsion.

What one learns pretty quickly about tomatoes is that fungicide is almost always necessary, AND it is a preventative, not a cure. That is, if you spray fungicide on affected leaves, the infection won't go away. Tomatoes can be pretty frustrating in this regard. Kind of amazing that tomatoes survived before people were around to spray fungicide on them.

Let me be frank. There are many things that can make tomato leaves look like this. But if you're not using fungicide, you ought to be.

Thanks again. This will be my third year planting tomatoes in this same space - have not had any noticeable disease like this in the past 2 years. Luck, maybe.

Yes, planting beds eventually get infected, and once they are, fungicide is needed. I think you can clean out a planting bed, fungus-wise, by just not planting there for a few years, but that's often very inconvenient.

Didn't realize that, will plan on that next year.

i would carefully trim off and discard all that lower growth before treating. take pictures after a few days to monitor the spread.. also note where it's starting/beginning. is it randomly on parts of the leaves, or does it start at the tips or edges then progresses inwards.. fungal diseases are usually very spotty, meaning they start on random parts of the leaves and not typically from one direction. the upper growth (top of image) that is starting to show symptoms appears to be starting at the tips, then uniformly progressing towards the base of the leaves, which could mean that it is not a disease, but a nutrient deficiency. as mentioned, i definitely would start with a fungicide treatment first.