Live in SC. My hibiscus come back each year. I have three plants and all three bloomed beautifully this spring. Two continue to bloom, but one is having problems. All the buds turn brown and die before they open. I've used Bayer Systemic but it doesn't seem to help. Some leaves have holes, so I've also tried Sevin dust.
Certified GKH Gardening Expert
It sounds like thrips. They attack the base of flowers and new growth, causing them to die. They can be difficult to see. The Sevin should help, but make sure you are focusing on the flower buds when applying. Here is more information: