ruthz,

I have experienced the same with my 2 brug. But it was a LOT more than 13 I lost.

For a while I thought it was that little horned worm....because every (or most) buds seemed to have a small hole in it. Almost as if the worm got inside the bud and ate the inside.

But I also thought it might be water. I sprayed and watered heavy for a few days and the dropping seemed to stop and the flowers came back.

Look to see if the buds have a hole.

Found more dropped buds today.
No holes in the brugs, but some of my rose buds had holes thru them and small round holes in the leaves.

Lack of water, Ruth...............the roots still need to be moist despite cooler temps.