Problem with roses
My neighbor has got a good-sized rose bush that has yellowing leaves. Each leaf is kind of two-toned, yellow & green. I told her I'd check it out. Thank you very much!
Multnomah County Oregon roses
Thanks for your rose question. Without a picture, I can only suggest a few possibilities, including a lack of nutrients (fertilizer), particularly nitrogen. Adding a complete or rose fertilizer will help plant, but not necessarily restore every leaf to green.) (See first picture.)
It can also be caused by a fungus that grows on the leaves, called black spot. (Second picture; more common in the spring but not unknown in the hot summer months.) Yellowing and browning can't be cured, but if any fungus is still alive on the leaves, an antifungal application such as Neem oil will kill it.
The plant can also be infected with a virus, called the mosaic virus (see third picture.) There is no cure for this, and the leaves should be removed and destroyed; it may spread (or already have spread) to the rest of the plant, in which case the entire plant should be removed.
Rose plants are also the hosts for a myriad of insects, which you'd only find by examining the plant carefully, including under the leaves and on the stems. Write back (with pictures) if you find any evidence of them.
Hope this is helpful to you.