Answer: Both of these plants are subject to stem rot caused by a fungal organism. Unfortunately, there is not much you can do to treat it except pull and destroy the affected plants. It is soil-borne and will be particularly bad in wet, cool spring and fall weather. I suggest pulling the affected plants and leaving the spot bare for the summer or putting in something that is not in the aster/daisy family. If you have an area with soil that drains better than the current site, transplant your flowers to that area, or create a raised bed to help keep their roots well aerated. Also, make sure you have plenty of circulation between plants so reduce further incidence of the disease. Hope this takes care of the problem.
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