canna lillies get a bacterial infection due to lack of calcium. You have to take the bulbs out and carefully check them. I found one link that says wash off bulb with hose dust with fungicide like Captan cut off soft area....some that are too far gone you might need to disgard.....if it is close to fall put them away in a cool dry place................when planting again next year use a different area. don't overwater....use 10-10-10 or 15-5-1 and a monthly all purpose fertilizer. Use leaves to keep the roots cool, plant in well drained area. This bulbs are from a tropical area and if you live in a cold area or cool area they need to be dug up and examined and put in a dry place to winter that they won't freeze.