All the leaves showing damage need to be removed from the plant. And water isn't the only thing they need so what and how much and how often have you been feeding them? Leaf tip death such as in your pics can be caused by excess nitrogen fertilizers or it could be a disease process. Since it appears to be only on the older leaves I suspect it is nitrogen burn but can't be sure without more info from you.

Dave

I don't see any lesions on the leaves.
Some yellowing and drying lower old leaves may happen without a disease.
I would trim them anyway especially if they are within a foot or so from the ground..
I am of the opinion that yellowing is due to excess water/rain ?

The next thing I would do is to spray with fungicide as prevention and/or to keep any disease in check.

Sey

Remove the yellowish / brownish leaves, but do NOT remove the lower suckers. Fungicide and mulch.