Roses can suffer from a variety of afflictions that cause their foliage to turn yellow, brown or red. If a plant's leaves turn red, the plant may or may not have a problem.
Anthocyanins are pigments that cause the petals of roses to turn red. Anthocyanins also exist in many berries, bromeliads and carnivorous plants.
A rose's stems and leaves also contain anthocyanins, which causes some leaves to turn red when the plant experiences a growth burst. These pigments protect young rose plants from UV rays, but as plants mature and no longer need this protection, the anthocyanins disperse and the reddish hue fades.
Not all rose leaves turn red. Various rose species contain different amounts of anthocyanins, and the plants react to these pigments according to their genetic traits. Growers accustomed to roses without this trait may fear their plants are diseased the first time they see their plants' leaves turn red.
The foliage of roses can turn red if a plant has rose rosette disease (RRD), a virus spread by microscopic wingless mites. Signs of RRD include excessive or aberrant growth, elongation of new shoots, branch clustering and leaf distortion.
RRD is incurable and fatal for rose plants. Afflicted plants must be removed from gardens to prevent healthy plants from contracting the disease. Organic rose miticides, available from companies such as Rose Pharm and Bonide, can help eliminate the mites that carry the virus.