As has been mentioned, good horticultural practices and selelection of
resistant varieites are the best method to minimize black spot and the other
fungal diseases.

Note that the scientific name of most of the fungal diseases include the
word 'rosa' in some form. These diseases are specific to roses and are not
transmitted from non-rose plants or trees.

Education and prevention are the operative words, good garden sanitation,
selection of resistant varities and if necessary a regular preventative
spray program will keep your roses healthy and disease free.

I have 'shovel pruned' a number of varities over the years,
the 'disease magnets' are just not worth keeping.

Just my $0.02 worth,

Tim