Roses have an undeserved reputation as being fussy plants. However, even easy-to-care-for varieties can suffer from the occasional disease. Roses can suffer from powdered mildew, leaf blight, gall, and a variety of afflictions that can cause their leaves to change colors. If a rose's foliage changes to a red hue, it may or may not mean that the plant has a problem.
The pigments in a rose that cause the petals to turn red are known as anthocyanins. Combinations of these pigments are what determine the hue of a rose's petals. Anthocyanins are also present in berries such as raspberry and blackberries that contribute to their hues as well as other flowers such as peonies. In fact, anthocyanins are responsible for reddish hues in many plants.
Anthocyanins are also present in a rose's stems and leaves. The presence of this pigment is why some rose stems and leaves turn red or bronze when they experience a flush of new growth. These anthocyanins protect the tender young rose plants from damage caused by UV rays. As plants mature and no longer need protection from the sun, the anthocyanins disperse from the stems and leaves and the red tint fades.
Not all rose stems and leaves experience this reddish tint because, just as in the petals of a rose, the stems and leaves of various species of roses contain different amounts of the pigment and react in different ways. Whether a rose stem or leaf turns red or bronze is a genetic trait. Some rose growers who are used to roses that do not produce red stems and leaves on new growth often fear that their plants have become diseased the first time they see roses with this trait.
Roses can also experience red foliage if they are afflicted by rose rosette disease. This disease, which is caused by a virus, affects each species of rose differently. Other indicators of rose rosette include rapid growth and elongating of new shoots, clustering of branches and distortion of leaves. The virus was introduced to the United States with the introduction of the multiflora rose. Multiflora roses, which are highly susceptible to the disease, were planted throughout the United States as a solution to soil erosion.
Once a rose contracts rose rosette, it cannot be cured. Once a rose bush has contracted rose rosette, it should be removed from a garden to prevent the spread to healthy plants. Diseased plants should either be burned or bagged and removed. Control the spread of mites that carry the disease with miticides.