I have heard the same thing Larry stated. But I've yet to lose a DL that was a rust bucket. And I have quite a few rust buckets in my yard. I have looked at mine closely at times and they did multiply and bloom well, but the leaves were very ugly during the growing season. Mine are put through drought stress and poor soil.
But I have had "dormant" plants that didn't survive but 2-3 years before they completely disappeared. They had rust, so maybe the rust contributed to their demise?
