By Amanda Sears
There have been several roses brought into the office in the past week exhibiting the same symptoms. These plants have excessive thorns and abnormal shoot development. Unfortunately, these roses are suffering from a disease called rose rosette.
Rose rosette disease may be found affecting roses throughout Kentucky. Its main host is multiflora rose, a thorny plant originally introduced into the United States from Asia.
The cause of rose rosette disease is a small eriophyid mite which carries the virus. Mites are transported on insects or by wind currents for up to 100 yards. The virus is considered systemic, meaning it affects all parts of the plant, even though you may see symptoms on only a few plant parts.
This pathogen is not spread by pruners or other mechanical means like some common viruses, but it is readily transferred onto rootstocks through grafts.
Early symptoms include increased growth of shoots with red coloration and distortion and dwarfing of leaves. Affected shoots appear to be more succulent than normal and they develop a proliferation of thorns. This abnormal overabundance of thorns is a useful field symptom for diagnosis, because the new shoots of many roses are naturally reddish colored.
Diseased shoots are not winter-hardy and will produce few blooms or the flowers may be deformed. Infected plants produce fewer roots than normal. The disease progresses to the rest of the plant until all the new growth is affected and the plant declines or is killed in winter. Roses may succumb in just one season, or symptoms may continue for another season or two.
Infected plants must be removed and destroyed so that the pathogen is not spread to healthy plants nearby. Care must be taken to avoid scattering disease-carrying mites to the other plants. Early detection is essential. Rose rosette disease affects the entire plant, but at the first indication of infection on a shoot, it might help to clip off the affected shoot in hopes that the rest of the plant is still unaffected. Multiflora rose could be a reservoir for the disease so they should be removed from the neighborhood of cultivated roses.
Educational programs of the University of Kentucky Cooperative Extension Service serve all people regardless of race, color, age, sex, religion, disability or national origin.