Q.What Is Wrong With My Pentas?
I live in southwest Florida and planted several pentas last March. Most really took off and did very well but some started dying off. Leaves start wilting and turning brown. I really can’t tell if it’s a watering problem or something else. I am attaching a photo below. I have tried trimming the dead and adjusting the irrigation system. Any assistance you can provide would be greatly appreciated.

Certified GKH Gardening Expert
This does appear to be a fungal/bacterial infection. This happens when the soil is not allowed to dry out some between watering, or it remains overwatered for extended periods.
From here, you will need a fungicide to treat this. This article will help you with fungicide use: https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
This article will help you to care for Pentas: https://www.gardeningknowhow.com/ornamental/flowers/pentas/growing-penta-plants.htm