should I
 

remove all the black spot leaves before spraying them? On some of my
bushes there wouldn't be much left and I wondered if that would
interfere with the stem development

Rose B

should I
 

wrote :
remove all the black spot leaves before spraying them? On some of my
bushes there wouldn't be much left and I wondered if that would
interfere with the stem development

I've read claims that so long as the leaves are still green enough to
function,
it just cripples the plant further to remove them. They're lost anyway once
black spot has taken hold. Try to kill the spores and halt the progress
with
the spray, and remove the fallen leaves.

Opinions? I vaguely recall having read that what I wrote above was
confirmed by scientific studies.

Now, for stems invaded by black spot, maybe removal would be the thing
to do...

Mark., been spraying with peroxide a lot to kill spores; seems to help
so far but I can't say for sure