This is another one of those problems I have not experienced yet CZP. I looked and wish I had an answer. But now that you brought it to my attention, I will research it and learn about it just in case it appears here...
thanks David, i tried looking for some more info but i can't really find anything.
it looks like it is an international problem in the canna industry and some people sound very upset about it. my cannas were just fine last year. literally no one on my street has them (surprising right), so i don't know what to think now.
That pic looks like white fly desease. When I had cannas they always had it and I sprayed and sprayed until I finally dug them all up and gave them away. They have so much water inside of them the bugs just love them.
They are hard to get rid of. I noticed some shoots coming up again from them. Oh well I'll leave them alone if the bugs leave them alone.
I'm in the country but we are not allowed to burn due to no rain so I put them in trash cans and my garbage men pick them up and they go into the digester and then onto dump.
Not surprised no one on your street has them. Mine were a pain.