Too much water could definitely do it. Also, if they are the older leaves and near the bottom, it can also happen. I would remove them. Maybe add some lime or organic fertilizer to your plants. Just be careful not to touch the stems.

Remove bottom leaves below fruit, healthy or not to reduce splashback and avoid disease transfer to upper leaves. Damaged leaves high up should also be removed. This is not unusual.

Don't touch the stems?

@ Capoman - You say it's not unusual, but what IS it & how do I avoid it moving forward?

Thanks

It can be fungal and/or bacterial infections caused by water splashing up from the soil or pests munching on leaves. Once leaves are infected, they can infect leaves further up. Most soils and many pests contain spores and bacteria that infect these leaves. If you leave them on the plant, they can infect leaves and fruit further up. It matters not which pathogen it is, the best way to manage it is to remove all foliage below the fruit and any damaged leaves higher up as many of these infections are initially local. Some wilts and stuff are systemic, and if so, not much you can do. But cultural practices such as removing lower and diseased leaves are just part of gardening and often can't be avoided. One other thing that can help a lot is to mulch your plants. This helps with the splashback issue as well as moisture control.

By the way, humidity does promote fungal growths. I don't think overwatering is the issue. Symptoms of that are usually wilting and yellowing overall.

Looking closer at your pics, are you using soil in your containers? If so, that would explain why you are getting infections. That's one advantage of many of using a soil less mix as you get fewer pathogens (and better drainage).

It's compost mulch that we get from our town mulching facility. Who knows whats in it I guess.

May want to check out the 5:1:1 soil less mix on the container forum. I've found it very trouble free and forgiving.

Appreciate the info.

I've been reading about the "Tobacco Mosaic Virus" - could this be it? My local nursery where I get my seedlings said something about a disease or virus on the plants up here (Connecticut/NY area) that come from down south. Can't remember what she called it, but she DID say not to use the cut leaves in compost piles as the disease (virus?) can stay dormant there and then return when the compost is used.

Or maybe the "Late Blight" I've been reading about? But those stories were really gloom & doom about the crop, and mine has been overall excellent....

I've had exactly the same problem and assumed it to be late blight. We have had an appallingly wet summer (haven't watered the Toms all summer). This was followed by a rise in temperature and minimal rain. This is when it appeared. I have removed one plant completely and all infected leaves (not to compost heap). I assumed I would loose all my tomatoes but nothing has got worse in 2 weeks so figures crossed.