Looks as though it might be rust. Remove infected leaves.

It would be helpful is you detailed the soil conditions where
your cannas are growing. Much of central Alabama soils are often heavy red clay
and these soils tend to lock up nutrients if the soil pH is not corrected. I
would first suggest you do a soil test at your local county extension office and
follow the recommendation given. They could also give guidance on the leaf
conditions.

The round circular necrotic lesions are very likely bacteria
leaf spot. This occurs primarily from dirt being splashed or splattered on the
leaves. This may have occurred when you were weeding. It would be beneficial to
put light mulch on the ground. I do not believe you have rust present as this
is primarily prevalent in hot dry weather.

As suggested above, you may want to remove and destroy the
leaves with narcosis. The pale green leaves should improve with proper
nutrition and warm sunny weather. Be sure to get the pH corrected.

Kent

I'm in prairie soil which is sticky, grey clay. I have had my soil tested at Auburn University and it is alkaline at around 7 - 7.3 which is why I keep lawn sulfur on hand. I will remove the affected leaves. You can't tell now, but originally, I planted one canna next to the fence and placed black, plastic edging about 3 feet from the fence and ran it about 8 feet along the fence because I knew the canna would multiply. The black plastic edging is still in the ground, but the cannas grew around it into the yard about 5 years ago and I stopped trying to control them. The discoloration does not hinder their grow or blooming. It is just unsightly. I have Cleopatra and Bengal Tiger in other sections of my yard and they are not affected at all. I think this one is Aida, but I can't remember. I got it at a plant swap.

Many semi-aquatic monocots, e.g., rice, can utilize large amounts of silicates in their cell walls and this is reputed to increase disease resistance. Cannas are semi-aquatic monocots. There is a granular silicate based lawn fertilizer, Excellerator, that I have used on my cannas and I have never had any disease or insect problems but, of course, that could just be a coincidence. See https://njaes.rutgers.edu/pubs/soilprofile/sp-v20.pdf. In any case, I can testify that 1 tsp./gal. of potassium silicate doesn't hurt cannas and a dried exudate appears on the leaves which indicates silicate uptake by the canna roots and xylem.