In small plantings, prompt removal of the "almost spent" leaves will prevent a lot of the crown rot from developing into a full blown problem. Here, I blame high humidity / dew, which runs down the leaf, to the base, where it's "trapped" by the leaf. The moisture can also make the bacterial rot possible, and, in many cases , here, I see both occurring on the same plant....I think the "fungal" opens up a wound that the bacteria can use to enter the rhizome. The "upside", for me, is that the fungal crown rot pretty much "cures itself"....sun, and airflow will halt it. I do spray fungicides, all year long, mostly for leaf spot, but, they will help with the crown rot, too.
