Quite often I am asked the question, "How can I protect my roses against blackspot?"
I am not an expert on chemical controls for Blackspot because we have never sprayed for insects or fungus in our garden since we planted our first roses in 1995.
The simple answer is to plant the "right" kinds of roses. Our roses are almost all "antique" and "low-maintenance" roses, and they have considerable natural resistance to fungal diseases. They do get mildew and blackspot, but they "do not take it personally".
I have heard of an organic control which is supposed to work pretty well, but I do not have a lot of personal experience with it. The recommendation is to get "Whole Ground Cornmeal" from a feed store (50 pound bags are pretty inexpensive), and sprinkle it on the ground around the roses. The presumed mechanism is that the cornmeal promotes the growth of "beneficial" fungus that crowds out the mildew and blackspot.
I hope to do some experiments with this method later this year, so check this page occasionally and I will update it to let you know what I find out about the cornmeal approach.
Good luck, and - "Keep on smelling the roses".
Last updated 04/06/2002