wee need clues please

indoors, greenhouse or outdoors?
pot or the ground?
prevailing weather -- temps and rainfall?
what have you done so far?
If you tried any remedies, what, when, and the results?
add anything else that might be helpful to us.

They're in a container. Weather is up and down. Late 80s during the day 70 or so at night. I haven't done anything I have no idea where to start. The plants get full sun for pretty much the whole day. I water every other day.

Looks like it could be a bit of septoria. I would remove the affected leaves and stems and use a garden fungicide for vegetables to possibly prevent its spread to more of the plant. Fungicides are best used as a preventative, before disease gets started, but you might be able to keep it from spreading to healthy leaves if you start a regular routine.

You live in a far different climate than I, but here septoria generally shows up when it's cool and rainy. It also tends to slow or stop after a while, but sometimes it just keeps going. Once it really gets going it's hard to stop. It's early yet, so you should try to stay ahead of it.