Rusty Brown Leaves on Canna

It's the first time I have cannas in my garden, so this is new to me. Don't know if it's a problem - some of their leaves turn a rust color then fall off. Can I stop it or is it natural?

Cannas are relatively pest free. Brown leaves can be the result of drought stress, excess water, or pests. Make sure the plants are growing in moist but well-drained soils. If this isn’t the case and the weather has been cool and wet – it may be a fungal disease. Remove infected leaves, make sure plants are properly spaced, and see if the problem corrects itself as the weather dries. Check for speckling or other signs of mites and aphids feeding on the leaves. If found, spray the plants with a strong blast of water or treat with insecticidal soap, Neem or other eco-friendly product labeled for controlling these pests.