Rose Rosette Disease (RRD) is a viral-like condition affecting roses, caused by the Rose Rosette Virus (RRV). The virus is spread exclusively by a microscopic pest known as the eriophyid mite (Phyllocoptes fructiphilus). Once a rose plant is infected, there is currently no known cure, making immediate action and prevention the only effective management strategies. RRD poses a significant threat to garden roses and typically leads to the plant’s decline and death within two to five years.
Recognizing the Symptoms of RRD
Identifying Rose Rosette Disease early is important, though symptoms may take weeks to nearly a year to appear after infection. An early indicator is unusually rapid, vigorous growth of new shoots that are bright red and fail to turn green as they mature. Unlike normal new rose growth, RRD-affected foliage remains discolored, distorted, and stunted.
One of the most distinct symptoms is the formation of dense, bushy clusters of shoots known as “witches’ broom” or “rosette.” These abnormal growths often exhibit an excessive production of thorns, making the canes appear hyper-thorny and sometimes thickened. The thorns on these shoots may initially be soft before hardening.
The leaves on affected canes may become deformed, brittle, or crinkled, often displaying yellow mottling or red pigmentation. Flowers may also be malformed, stunted, or fail to open completely. The combination of excessive thorniness and witches’ broom helps distinguish RRD from herbicide damage, which can sometimes mimic leaf distortion.
The Required Action: Immediate Removal and Containment
The Rose Rosette Virus moves systemically throughout the plant, including the roots, so pruning individual symptomatic canes is not an effective treatment. Upon confirmation of RRD, the only reliable course of action is the complete removal and destruction of the infected rose. This must be done immediately to prevent the mite vectors from spreading the virus to nearby healthy plants.
To contain the mites during removal, carefully cut the entire plant down to the base and cover it with a heavy-duty plastic bag before digging. Remove the entire root ball, as the root system can harbor the virus and potentially infect subsequent plantings. All removed plant material must be sealed in the bag and disposed of off-site, such as at a landfill.
Infected plant material should never be composted, as this will not kill the virus or the mites. Following removal, all tools, including pruners, shovels, and gloves, should be sanitized immediately. Use a 10% bleach solution or a household disinfectant to clean equipment thoroughly, ensuring no mites are transferred to other roses.
Preventing Future Outbreaks
Long-term management of RRD focuses on controlling the eriophyid mite vector, which is easily dispersed by wind and can travel on clothing or tools. A primary cultural practice is the removal of wild roses, such as the invasive multiflora rose (Rosa multiflora), from the surrounding area. These wild species serve as a major reservoir for the virus and the mites.
Proper spacing between cultivated roses is an effective preventive measure. Since the wingless mites must crawl or be blown, spacing roses so their foliage does not touch significantly reduces mite transfer. Using mixed plantings, where non-rose shrubs are interspersed, can also create a barrier that slows the vector’s spread.
Chemical control involves the targeted use of miticides, as standard insecticides are often ineffective against eriophyid mites. Products containing active ingredients like bifenthrin or abamectin are used, often applied in the spring as new growth emerges and again in mid-summer. Horticultural and dormant oils can also be applied in late winter or early spring to eliminate overwintering mites.
After removing an infected rose, clear the planting area of all debris. A waiting period of at least one year, and ideally several years, is recommended before replanting in the exact spot. This ensures that any lingering infected root fragments die off. Also, avoid using leaf blowers near roses, as the strong air currents can carry the microscopic mites onto healthy plants.