Radika Kesavan writes:

Which fungicide has this effect on your Summer Snow? I am asking just
out of curiosity - have never heard of this phenomenon before. And is it
only SS that has this reaction to that fungicide? Also, does SS react
like this only to that fungicide?

Any of the fungicides that I have used have this effect on SS. I have probably
tried 7-8 different brands over the years. It took some time to fugure out why
the leaves were curled, but I noticed after a time that it only happened right
after I sprayed. The only rose that reacts like this is Summer Snow. The
leaves don't burn, it's as though it's thinking, "don't spray that stuff on me"
and curls up to protect itself.
It doesn't have a big BS problem, so I stopped spraying this one.