I'm using a copper based fungicide on all my plants. All will look fine, then I will come out in the morning and a lot of the plants have still been hit with the fungus - blackend leaves, dried up stems and blackened and dead beans, peppers, watermelon, etc. Overnight I lose half my plants or veggies. WHY!!!
This sounds more like a spray problem than fungus problem to me. The copper based fungicides can and will cause severe burn on the foliage of some plants. The amount used in a given spray mix must be followed without change depending upon the plants being sprayed. I would suggest changing to a more earth friendly fungicide if it truly is a fungus problem, such as a product called Green Cure, available on line at a site called Planet Natural. There could also be neighborhood dogs or wild animals spraying their urine upon your garden area overnight, thus causing these issues come morning.
My first question is, "Are you positive you are using the proper product for the diagnosed problem?". Second question is, "Are you using product as directed on the package?". If both answers are yes, I would suggest that you take samples and product to your local agricultural extension office for consultation, identification and recommendations.