Heat wave cause this sunflower to go bad?
I have this full grown sunflower, I bought at a nursery instead of raising it, and it was not getting sun. Then we had the heat wave in San Francisco, and I decided to trim a leaf, and I found this, please see photo. I know it must have been going bad before, but I never noticed it until now. This is the worst leaf, and some of the other have less of these brown spots. Can it be saved with treatment like my roses, or does it have to be destroyed? I have never seen anything like this before.
Here is a link that might be useful: link to flickr with sunflower leaf