Question
I am located in Southeast Texas, about 100 miles north of Houston.

My rose bushes are healthy with good leaves and stems.  However when the  rose bud starts opening the edges of the petals turn black and continues to grow, spoiling the beauty of the rose and making them unsuitable for using as cut flowers.

I spray regularly with a fungicide purchased for rose disease control.  I fertilize early in year with rose fertilize and add Epson Salt about every 3 months.  My beds are raised and well drained and consists of sandy soil and leaf mulch.

Can you offer any advise as to what is causing this and how do I stop it>

Answer
There is a tiny little winged insect called a rose midge or capsid bug. These very small insects lay their eggs at the base of a rose bud and when the eggs hatch, they feed on the buds which causes them to be damaged or just blacken and not open. A rose midge is a bright green bug and if you take a piece of paper and tap the end of the rose on it, if they are still there, you will be able to see them. Any insecticide will get rid of them just follow the directions on the package.
However if you have sprayed your roses with an insecticide then another reason would be that when the weather is very hot and the rose bush doesn't get enough water. Red roses  plus multi coloured ones are very prone to burning in hot sun no matter what you do. A thick mulch would help as roses love cool roots and the much keeps the roots cool and damp. Hope this helps. Lynnette