Powdery mildew - Rudbeckia hirta and soil

Chapel Hill, NC(Zone 7b)

I have a huge number of self-sown R. hirtas (originally wintersown). I love them when they are healthy (of course) and in prolific bloom. BUT - after a while some of them start wilting, flowers shrivel, stems and leaves turn light brown and sort of fuzzy looking. I guess that is powdery mildew?

I am going to pull them all out. Now my question is: does the mildew remain in the soil and if so what can I do to get rid of it. If there is something that I can use (preferably nothing too toxic), can I immediately put in vincas, or should I just leave only mulch in those spots?

Has anyone heard of using milk spray? See the URL below


Thanks for your ideas,

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