Viral diseases of roses are generally diagnosed based on symptoms. The diseases usually do not kill infected plants but may reduce plant vitality and the quality of flowers. The leaf symptoms may include yellow mottling, yellow or white veins, banding of veins with various colors, yellow to light green blotches or lines in the leaf, ring patterns, distorted or puckered growth, and smaller than normal foliage. Because of the wide range in symptomology, it would be helpful to find pictures of rose viruses to help determine whether a virus is really involved. Many horticulture publications have such pictures, and the Web is very helpful. Report on Plant Diseases (RPD) No. 632 discusses the rose viruses. The Compendium of Rose Diseases by APS Press has great detail for avid rosarians or diagnosticians.
Virus particles will not grow in artificial media in a lab. The Plant Clinic cannot isolate a particular virus through culturing procedures. Viruses are too small to be seen with a light microscope, so thin sections of plant material are not of any help in pinpointing a virus. For those who have to know the exact virus involved, there is a private lab in Indiana called AGDIA, Inc. They can do a rose virus screen testing for eight viruses, as detailed on their Web site http://www.agdia.com/. There is a fee for this service, so check the Web site before sending your samples.
Virus infections of rose are systemic, which means they will be found in all plant parts. Parts of the plant may remain symptomless, despite the infection. Plants do not have an immune system; and they will retain the virus as long as they are alive, with the exception of heat treatment in commercial propagation, which is used to inactivate some of the mosaic viruses. The virus particles need a live host to replicate. Although it may appear that viruses are more intense in the spring and fall, they are present all year. The heat of summer inhibits virus activity.
Because the treatment of rose viruses is generally the same regardless of the specific virus involved, exact identification is not usually necessary. Viruses can be confused with injury caused by growth-regulator chemicals. The pattern of injury and host range should help in diagnosis. Herbicide injury will be most intense near the source and less intense moving with the wind or water away from the source. Broadleaf herbicides such as 2,4-D or dicamba should also affect other broadleaf plants in the area. Rose viruses (especially the mosaics) are spread primarily by budding and grafting. It is rare to spread such viruses by insects, plant contact, or seed. Therefore, the pattern of infection in the planting would be very different from herbicide-drift injury.
The general recommendation for control of rose viruses in the home garden is to remove infected plants. Because these viruses are spread almost entirely by budding and grafting, the responsibility for control should lie with the nursery and commercial rose grower. If you purchase a plant that develops virus symptoms, contact your supplier and ask for a replacement. When buying plants in a retail center, examine the plant closely for virus symptoms.