In article , elfa
wrote:

In article , Cass says...

In article , Mark. Gooley
wrote:

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.

Yes, the non-stripping was the opinion of a Texas plant pathologist
back in the late 70's, from what I read he

http://www.rosekinggardens.com/faqs/blackspot.htm

Makes sense.

I was amazed by what he said about removing the fallen leaves that have BS on
them:

"Fallen leaves. Dr. Lyle concluded, "Fallen leaves on the ground or top of the
mulch are not a source of carryover of the disease, even though this is a
frequent belief. As soon as the diseased leaves fall and start to rot, the
blackspot disease also decays. There is no need for removing the mulch that
remains from season to season. Just add more to it as needed."

According to the way I read it, no real need to remove the leaves from the
ground.

Maybe not for blackspot - that I can't address, as I have little here -
but it is not true of rust, which does overwinter. So I think the broad
statement is not correct, *if* it is correct for blackspot. I didn't
quote the article as an advocate, btw. I just was reporting the
research, that it is old, and the source.

Everyone in the past 300 years has recommended cleaning up under roses.
The persistence of spores is the primary reason. And blackspot isn't
the only fungus - anthracnose, rust, powdery mildew, cercospora,
botrytis, brown canker, brand canker and other things that go bump in
the night.