Staff at the University of Illinois Plant Clinic can identify most diseases. Fungal and bacterial isolates confirm the presence of those pathogens. Viral diseases are a different case. Virus particles will not grow in artificial media in a lab, so they cannot be isolated 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. There are a few private labs where serological tests can be done for some specific viruses. One example is AGDIA, Inc., a private lab in Elkhart, Indiana. The Plant Clinic frequently uses AGDIA testing services to supplement diagnoses. They provide a rose virus screen, testing for eight viruses, as detailed on their Web site, http://www.agdia.com/. There are additional virus tests available for rose as well. There is a fee for this service, so check the Web site before sending your samples. Also, read on to see whether you need to know the specific virus.|
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 symptoms, 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 Disease (RPD), no. 632, discusses the rose viruses. The Compendium of Rose Diseases by APS Press has great detail for the avid rosarian or diagnostician.
Viral infections of rose are systemic, which means they are found in all plant parts. Parts of the plant may remain symptomless despite the infection. Plants do not have an immune system, and they retain the virus as long as they are alive. Heat treatment in commercial propagation is used to inactivate some of the mosaic viruses before increasing plants. 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 still present all year. The heat of summer inhibits virus activity and masks symptoms.
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 is 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. When buying plants in a retail center, examine the plant closely for virus symptoms.