I inherited a stand of orange & yellow canna (Konigen Charlotte?) with the house I bought last summer. I love the plants but have been disappointed by the rapidly wilting/dropping flowers. Within a day or two of blooming they turn brown & fall off. They've also been eaten by Japanese beetles but this seems to be a separate issue. Is this normal behavior or are the plants suffering from a disease? They're planted in a bed next to the house that stays wet to moist most of the time thanks to a nearby sprinkler head. I've treated them with an organic fungicide & insecticide with no results. The leaves & stalks seem healthy & they've produced plenty of blooms. I live in SE Virginia & the plants stayed in the ground over the winter. Any advice will be greatly appreciated.