Answer: White flies may congregate on plants but they don't leave a fuzzy weblike mass on the leaves. I think your canna lilies have mealybugs in addition to the white flies. Mealybugs have a waxy coating that looks fuzzy. You can pry these insects off your plants with your fingernail. Since it is late in the season, I wouldn't try to treat the problem with chemicals but I would cut the tops of the plants down to ground level. This will get rid of both insect problems. Your cannas will resprout healthy new stalks and leaves.
Best wishes with your garden!
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