The leaves of a canna plant can be just a beautiful as the flowers that bloom on it. They are large and look like leaves on a banana tree. But bugs and insects threaten these leaves, with caterpillars, slugs and snails being the worst enemies. If these get on your leaves, they will eat right through them, leaving rows of holes. By taking a few preventive measures, you can keep your leaves healthy.
Search the surface of the canna leaves to remove any snails, slugs, caterpillars, or eggs already on the leaves. Search underneath the leaves as well as areas near the stem. The eggs will be harder to find. A good indicator that an egg is on the leaf is that the leaf is curled.
Remove canna leaves that already have holes.
Spray each leaf with an insecticide soap that contains Bacillus thuringiensis. Use the insecticide once per week to prevent any future attacks. If you like, you can rotate your insecticide spray between Bacillus thuringiensis, Orthene, and Sevin. By rotating all three, you will decrease the chances of the bugs becoming immune to the treatment.
Remove any debris, such as dead leaves, mulch, paper, and gardening tools, from around the canna, since the snails and slugs like to hide underneath the debris.
Place snail bait around the base of the plant. Purchase this product from your local garden supply store.
Make a "beer trap" for the snails/slugs if you don't want to purchase bait. Cut a hole in the side of a small plastic container. Place the container on the ground around the plant. The container should be low enough to the ground for a snail/slug to crawl into the hole. Pour several inches of beer into the container and cover it with a lid. Check the container every day to remove dead snails/slugs.