I've been in the same house for 2 years now. I have 6 rose bushes in the
same area. Five of them are great. One of them, a red bush, continually has
thinner branches, and leaves that turn yellow/droop more than the other 5.

I'm in Southern California, the plants get great sun.
Each year I've pruned the bush down and it comes back up the same. The tree
has probably been in the ground for years. When pruned down it looks just as
healthy as my other rose bushes. I don't give my bushes anything other than
water, I have good soil and get great roses on all bushes but this one.

Is there any chemical I can treat it with that might fix any disease it has?
Or would best to replace it since it's that time of year?