Q.Why are rose buds turning brown & dropping off when the plant looks healthy?
Rose plant looked very healthy with shiny leaves when I bought it. In spite of weekly
spraying with 3–in-1 rose spray (insecticide, fungicide, black spot), it has now
got totally brown buds that fall off & no new healthy buds. Leaves are still green.
It has gotten plenty of rain this summer. What’s wrong?
The amount of spraying could be too much and is having a negative effect upon the overall rosebush. Too much rain can actually cause the buds to get water logged, sort of rot, turn brown and fall off. Here is a link to an article I wrote on roses not blooming that may be helpful to you as well: https://www.gardeningknowhow.com/ornamental/flowers/roses/no-blooms-on-roses.htm