"Jim Carlock" wrote in message
.. .
Somewhere, I have recently read that planting chives next to
roses will control the black spot. I don't know how true this
is, but unless someone else indicates negatively, it might be
worth a try.

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*Some* studies have shown that planting garlic chives next to roses will
deter spider mites. It does nothing to prevent fungal infections. Black
spot is mostly carried over and reproduces from lesions on the canes, so no
method that doesn't involve coating the canes and leaves with some substance
will stand a chance of working as a preventative.