You probably have the dreaded leaf rollers. Sevin Carbaryl dust kills them on contact. Try cutting off the stalks that are infected and then dust the remainder.

You have more options.

Here is a link that might be useful: TweetyPye's pic

My cannas looked like that every year. I started using very, very diluted pyrethrins at dusk when I saw the first sign and they looked pretty good for a long time. Pyrethrins seemed like the best option to me because it can be very specifically applied and only affects the insects it actually comes in contact with. Bt on the other hand affects all caterpillars and must be applied as a dust; the thought occurs to me that there is less control with a powder than a liquid and that scares me a little. I'm sure that's unfounded but it made sense to me, anyway. I finally took out all my green cannas because they seemed to be more affected than the colored foliage ones. If the dark ones start looking like that, though, they're out of here.

Thanks folks, for all your advice. I cut the affected foliage out of my cannas today and treated them. I saw lots of tiny white butterflies, flying around them, so I am sure leaf rollers are my problem.

Be sure to cut down and dispose of all the dead folage in the fall. This seems to help mine. I read somewhere that they over-winter in the decaying leaves. I still had some this year, but not as bad. I sprayed right down in the rolled leaves and now they are starting to open and recover, although I have to break the threads on some. Keep an eye on them - I still have some showing up.

I find dropping one or two drops of mineral oil in each new leaf as soon as you can fit a dropper into the tip works wonders. Also, fall leaf clean up of cut foliage is a biggie as far as controlling them. A lot of work when you have as many Canna's as I have, but well worth it for the beautiful results.

I agree with the fall clean up. I have seen no leaf rollers this year, and a few years back they were terrible, so I guess disposing of the stalks quickly really has helped. If I do see any, I will cut it back and let the plant start over. They grow so quickly its no big set back.

I'm happy to report that my canna's are recovering and looking great! I'm beginning to get some blooms already. Thanks for all your suggestions. This really is the place to get answers to your gardening problems. I had never had "leaf rollers" before, so had no clue as to what my problem was, and as always, you guys came through for me! :)