What you describe on the corn sounds like it might be parasitic nematode damage to the root systems. Nematodes are very common in Florida especially in sandy soils.

There are several species of nematodes and the symptoms represent differently for each type. I'd pull up one of the affected plants and inspect the roots.

Here is one publication describing nematode damage in Florida vegetable gardens.

Nematode Management in the Vegetable Garden

About your peppers, could it be sun-scald? Have they just been set outside in the sun without hardening them off? Give us a bit more information, in-ground or in pots, type of soil or potting mix, etc... Was there a big change in anything that could affect them right before the leaves started to turn brown?

On top of what everybody else said, I can't help but notice you mentioned that you water twice daily. How warm has it been there? Here that would certainly be overwatering, assuming our soil type. But if it's a sandy soil I can see it being necessary.

Ask in the Florida gardening forum. I'm south of you, but still considered zone 9B - 10A. I've just cleaned out my vegetable garden for the summer, not sure what planting times are further north, but the UF website has lots of information (google UF vegetable gardening). Nematodes could well be the issue which is why most Florida vegetable gardens are raised bed and container gardening.

I'm in central FL as well. I'm still learning, but have found that planting TONS of french marigolds around my plants, and only watering in the early morning has helped keep my garden alive.

It sounds like you may be gardening in muck. Sometimes when they dredge wetlands, they put that soil up on the empty lots. It's not great soil, even though it's black. The best thing you can do is to have your soil tested at your local extension service. Every county has one. They can tell you what kind of soil you have and how you need to amend it, and you will have to amend it if you ever want anything to grow well in your garden. Also, look at the Florida Vegetable Gardening Guide from UF/IFAS to find out what time to plant what in your area. It has a lot of excellent information that can help you.

Yes, forget everything you know about gardening up north. We garden in the fall and winter, some in early spring, not much in the summer.