Time to act:
A viral infection, for which, sadly, there is no cure. Some cannas seem able to shrug it off, but it has the potential to spread quickly from plant to plant, so it's best to remove and dispose of affected individuals at the first sign of trouble. It's not confirmed how the virus is spread, but sap-sucking insects, nematodes and gardening tools, such as pruning knives, are likely contenders.
Canna leaves develop pale spots and streaks, as well as a distorted, crinkly look, while flowers may also become distorted and exhibit white patches.
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