Caterpillars or larvae and brown moths
Our cannas have been decimated this year. At first look you would think grasshoppers, but have not seen any this year. It was not the canna worm that puts bullet like holes in the leaf. Going out in the morning there were hundreds of brown moths flying around them. We decided to just cut them down because we didn't know if they would attack some other plants and in the process found whitish larvae in white webs on the underside of some leaves. So far have not seen them on any other plants, accept a few small white webs on perennial hibiscus. Any comments, id of these moths, how to treat would be greatly appreciated.
Certified GKH Gardening Expert
You most likely have a webworm infestation. These are a group of moths whose caterpillars form webs. Several of the species will eat cannas. Removing the plants and removing all the webs and larvae you can see is a good idea to prevent them from spreading, since they will eat various shrubs as well. See these articles for advice: