I wouldn't worry about the very lower leaves turning yellow. When you let the plant to grow on its own(no pruning , no trimming) eventually some leaves have to go. On top of that too much rain, I trim all such leaves, especially if the are less than 10" from the ground. I think you are doing the right thing by NOT fertilizing. I would 've done the same. Let them start bearing some fruits then give them a light dose.

Your bamboo looks like it's in rocks. I'd say water MORE, or at least to the point where the water is above the rocks. If it's in direct sunlight, take it out. Dracaena Sanderiana is a member of the lily family and native to the rainforest. It's used to indirect sunlight, so this could be a problem too.

I think I know what you mean. After plentiful rain and then scorching sun, plants can do this; it can be quite dramatic in its effects. Not sure what it is, but I don't think it's just leaf streak. Could be Midwest Malaise fungus. You should provide a picture. I would just trim back and hope the plant survives. Sounds as though they are still blooming well.

Please see your other 2 threads -here- and -and here-