I often have this problem on bottom leaves ,used to think it was normal senescence until a few plants died, seem to recall it's mites or thrips or some other sucking insect.

I sprayed with neem. I don't usually spray, but last year for the first time I had fungus on my peppers, and folks said I should spray BEFORE the fungus if I wanted neem to work.

This does not seem fungal, but I'm not sure WHAT it is. These plants are begining to bear fruit, are in self watering containers, and it is very hot and dry here.

Here are some pictures.

Can you see that little guy? Reminds me of a grasshopper.

Underside

This is probably the most characteristic leaf.

Here is a web I saw.

Close up of what might be something different.

End stage. Not sure the leaf on the left is yellow for the same reason.