Last night I discovered that one of my rose bushes had developed the disease
Powdery Mildew. So today, I proceeded to cut off all infected parts, which included stems, leaves, and rose buds that had not yet bloomed. I had to cut off a lot of buds, which was a shame, as I have never had that many buds before and they would have been very pretty when they bloomed. But they had to go, otherwise the infection would spread. I then bought this expensive fungicide from Home Depot. It was a super concentrate, only 1 tablespoon per gallon of water was needed according to the directions. It had a strong bad odor, even in its diluted state. I sprayed down what was left of the entire rose bush, including leaves, stems, fully developed roses, and rose buds. Hopefully the fungicide works and there are no reinfections.