What's happening to my plants?
The leaf blights on the tomato and pepper may be from a fungus that causes a disease called late blight. The leaf blight on the melon might be a fungus called Alternaria. However, you might consider taking these leaves to your local extension office and asking to speak with the vegetable or horticulture agent. The Hendry County office website is: http://hendry.ifas.ufl.edu/. In the meantime, pull off the affected leaves and throw them away (don't compost them or leave any in the pots or on the ground nearby), and avoid watering the plants with a spray that wets the leaves. Make sure they get plenty of sun and space the pots so that there is plenty of air movement between plants.