Q.Why Are The Petals Of Gerber Daisy Turning Brown Before Fully Opening
In zone 7. Planted outside for numerous years.

Certified GKH Gardening Expert
Many times, bud blast can be brought about by environmental conditions. My opinion on this one, given the age of the plant, will be Botrytis blight.
Here are some articles that will help:
https://www.gardeningknowhow.com/plant-problems/environmental/bud-blast-in-flowers.htm
https://www.gardeningknowhow.com/plant-problems/disease/treating-botrytis-blight.htm
https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm