Cucumber and zucchini plants tend to get diseased after a few weeks of production, no matter what you do. Both are susceptible to mildew, cucumbers will get bacterial wilt from cucumber beetles, zucchini can get attacked by vine borers. You can check the base of your zucchini plants for holes and an orange frass. Dig inside and you'll find the larvae.

I succession plant every 2-3 weeks and when the plants look bad i tear them out. You may want to try a fungicide on your plants, especially in the type of wet weather you're dealing with. Liquid copper or Serenade, or some have had luck with homemade fungicides made from baking soda or milk. It won't cure the disease, but will help protect any new growth.

If it's bacterial wilt, there's no cure for that. Infected vines will die. It's very common with cucumbers; one bite from a cucumber beetle is all it takes.

In FL at this time of year there's also the dreaded pickleworm in addition to all the other problems. This just isn't the time of year for most of us to try these plants because of all the disease/insect problems, also production slows way down when the heat and humidity really kick in.

If you haven't seen it, the U of F's Agricultural department has an excellent guide to vegetable gardening in FL, including when best to plant:

Here is a link that might be useful: IFAS planting guide