I have three pink rose bushes. I think they are knock out, I did not plant them. The last two years the blooms turn brown and doe
What is causing my roses to turn brown and not open up?
It sound like you may have an insect problem. Rose curculios are easy to spot so we can rule them out. Thrips and rose midges are very small and hard to find. Thrips suck the juice from buds and rose midge eggs are laid inside a developing bud. Both cause the bud to fail, turn brown and fall. Here are articles on rose midges followed by thrips: https://www.gardeningknowhow.com/ornamental/flowers/roses/rose-midges.htm. https://www.gardeningknowhow.com/ornamental/flowers/roses/rose-thrips.htm
The internet is full of potential control measures. Using systemic insecticide will harm good and bad bugs, including bees, so it is reserved for severe infestations.