You've got canna leaf rollers
-Two caterpillars, in particular, are very destructive to canna, the larger canna leafroller, Calpodes ethlius
, whose adult form is variously called the Brazilian skipper, the canna butterfly, or the arrowroot butterfly and the lesser canna leafroller, Geshna cannalis
. Chemical control is inneffective because larvae are protected from direct chemical exposure within their leaf rolls. If you want to treat your plants with something, then Bacillus thuringiensis (Bt) products are the best choice for control. Follow the application instructions on the label of the specific Bt product. Mix in a couple of drops of liquid soap to help the mixture adhere to the leaves. You will need to try to get the mixture into the leaf rolls. I would also suggest simply cutting off the leaves that are rolled or that you see symptoms on. If you have a really bad infestation, simply cut the plants down completely, feed them, and let them come back up.
Here is a good website that describes their life cycle: