Yesterday, I noticed what appeared to be a water-soaked area on the tip of one of my Canna leaves. This morning, it had gotten a little bigger and is starting to curl. The area is soft, not crispy at all. It receives early morning sun and then full sun from about 10am until about 1pm and filtered/dappled sun after that. Then it receives a little full evening sun as the sun goes down over the house. I water the Canna every morning and sometimes again in the afternoon if it was a really hot & sunny day. No pesticides or herbicides have been sprayed at all. As of now, this browning is only happening on the tip of one leaf and only on this one Canna (There are 4 more near it that are just fine.) No spidermites or other insects on the top or bottoms of the leaves as far as I can tell. Is it possible I am watering it too much or not good enough? Any ideas as to what is happening?
Based on my limited experience with Cannas and knowledge of your growing climate, watering daily is excessive.
The only pests I've had to deal with eating Cannas are snails and slugs however they normally don't damage just the tip of the leaves.
I'm in a drought state and my cannas get partial sun in the morning and evening sun in the afternoon. Our winter was mild to hot. I've only had to water my cannas 3 times a week. They're over 8 feet tall and have bloomed all year.
We have really sandy soil here & I've done my best to amend with compost, but I just can't seem to find anything that will retain the moisture in the soil. That is the reason I have to water so much (and the lack of rain). Don't recall fertilizing them in the last week or so. I'm kind of leaning towards the soil probably not retaining the water I give it. If other leaves start browning, I will just dig one up and check the moisture in the hole.
I have very sandy soil here on West Coast of Scotland and the only way to amend the soil for growing Perennial Plants is to get hold of as much well rotter Horse manure, this must be well rotter, by that it needs to have been piled up in a heap and turned every so often, when you approach the heap these should be no strong odour, IF you take a handful of the pile, you should be able to crumble it between your fingers and thumb, it should look dark brown like a good dark compost.
Most places that keep horses (riding school / stables etc) give the manure away for free so long as you can take it away yourself, some places bag it and deliver to you at a cost. IF you can, go get it yourself as that way you will get well rotted stuff, It's easier to get large amounts end of winter when horses have been inside at night, the stables are cleaned out and even the straw is composted down, after rotting down, all the acidic matter is gone and it is already rotted.
IF you can only get fresh manure, it's still OK IF you have an area in your yard to store / pile it yourself and throw plastic cover over it to keep rain and wind off it, this way the manure will heat up and perhaps rot down even faster to be ready for use the end of season or beginning of spring.
There are other additives like Home Made compost, store bought compost purchased in large bags etc.
Looking at the brown tips, this looks to me like some form of liquid, like pesticides, have you sprayed recently as maybe some got blown in the wind, OR lack of moisture at the roots,
Stick your finger into the soil or scrape a little soil away close to the Root /Tubers, this will let you assess IF the plant is suffering from water shortage. IF it is water shortage, try dig a hole close to the tuber, stick a clear plastic juice container into the hole after you remove the bottom of container. when you water, fill this clear container a few times and this will get water right down to the soil around the root's where it's mostly required. this will maybe help until you can amend your soil.
OR lift the plant, fill a pot with good compost and replant the pot with the Canna, sink the pot into the soil and water the pot, maybe this will help the plants IF lack of moisture is the problem.
Hope this helps you out a little and things improve soon.
At this point I would mulch with whatever organic sort of material you like. Fine to medium bark chips, shredded bark, tree company chips... DEEP.
Cannas are OK with lots of water, they will even grow on the edge of ponds. They are also OK when they are established with very little water. I have them in both places: In the stream that leads to my pond and in an area that I never water.
In sandy soil, and newly planted plants I think you are doing right to check them daily, and probably water daily.