Answer: Unfortunately, Rudbeckia is prone to many diseases. Specifically, Crown and root rot, Botrytis, Anthracnose, Gray Mold and Stem Rot, Mildew, and Rust. Rhizoctonia root rot, sometimes called charcoal rot, sounds like what may have attacked your plants. Remove and discard them now and if you decide to plant new ones next year, plant them in a different spot so you won't have a similar problem.
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