Hi chelsea714!!!! Mini roses
are prone to powdery mildew, spider mites, and aphids when grown indoors(also need constant humidity). It is a good idea to plant
them in the ground as soon as possible and they will come back each year. You can prune them back & they will grow new leaves all spring
& summer. I just pop the old blooms off with my thumb and forefinger. Mine have been in the ground for 4 years so far & come back every year just as pretty as the first. I will admit I killed 2 other mini roses
before I really knew how to take care of them, they both got spidermites in my house, don't know how but it really frustrated me. So I decided to buy 2 more & plant
them outside immediately & they have been growing
great ever since.Your problem sounds like powdery mildew.You can try to rinse the leaves off underwater, but I think the best answer is to plant
them outdoors, they require A LOT of care indoors, and require little care outdoors.