Help!

Two weeks ago, I sprayed three rose bushes (one Buttercream HT, and 2
JFK HT's) with a copper sulfate solution. I had looked up on the bottle
the proper water:chem ratio, so it should have been correct. A week
after I sprayed the roses, it snowed here in NC. The snow only lasted a
few days, and we've had temps about freezing lately.

This week, I noticed that my 2 JFK's look good, but almost all the
leaves on my Buttercream have turned brown. It looks like it is ready
to kick the bucket.

Was it the copper sulfate solution? Was it the snow? Is this normal,
and will my rose bush recover? Should I prune it down to help it out?

Thanks in advance!
Heidi

Raleigh, NC