Just found an article at Underwood Gardens http://underwoodgardens.com/news/wmview.php?ArtID=13 that discusses compost tea use for black spot in roses. The study was done at the Institute and concludes compost tea is a better alternative than other treatments, and why. Very interesting.
Institute for EcoSystem Studies
Thanks! I love it when nature takes care of her own. I booked marked the site for next summer when my neighbor's roses get black spot again.