Rose Rosette Disease (RRD) is a destructive and incurable condition that poses a significant threat to all species and cultivars of garden roses across North America. First identified in the 1940s, this serious plant disease causes dramatic and disfiguring growth abnormalities in infected plants. Since there is no known cure, RRD inevitably leads to the decline and eventual death of the rose, often within two to five years. Recognizing and acting quickly upon symptoms is urgent for maintaining the health of ornamental gardens.
The Rose Rosette Virus and Its Vector
Rose Rosette Disease (RRD) is caused by the Rose Rosette Virus (RRV), a negative-sense RNA virus belonging to the genus Emaravirus. RRV is systemic, meaning it spreads throughout the entire plant, including the root system. The primary means of natural transmission is a microscopic pest known as the eriophyid mite, specifically Phyllocoptes fructiphilus.
These mites are tiny, worm-like arthropods invisible to the naked eye. The mite acquires RRV after feeding on an infected rose and transmits the virus to a healthy plant through its feeding activity. While mites can crawl short distances, they are primarily dispersed by wind currents, which allows them to be carried over long distances. The virus can also be spread through grafting. Mites can be carried on tools and clothing, but the virus is not typically spread by pruning shears alone.
Identifying Key Symptoms
The most characteristic visual sign of RRD is the formation of a dense, brush-like cluster of shoots known as a “witches’ broom” or “rosette.” This abnormal growth results from an excessive proliferation of small, stunted shoots emerging from a single point on a cane. The new growth often displays an unusually bright red or magenta coloration that fails to mature to a normal green hue. This color is a key distinguishing factor from the naturally red new growth of many healthy roses.
Infected stems may also exhibit a noticeable increase in the number of thorns, which can appear softer and more pliable than normal thorns at first. Leaves within the witches’ broom are typically distorted, curled, stunted, or may show a mosaic-like pattern. Flowers on diseased canes often become malformed, discolored, or fail to open fully, sometimes emerging in tight, stunted clusters. Symptoms may initially appear on only one cane but will eventually spread throughout the entire rose bush.
Prevention and Management Strategies
Since there is no effective chemical treatment or cure for the Rose Rosette Virus, management focuses entirely on early detection and removal to protect neighboring roses. The most important action is the immediate removal of any suspected or confirmed infected rose, including the entire root ball. The infected plant should be placed into a sealed bag before being dug up to contain any mites, and then disposed of off-site in the trash.
Pruning out symptomatic canes is ineffective because the virus is systemic throughout the whole plant. To reduce the risk of future infection, remove any wild Rosa multiflora in the vicinity, as this invasive species is a common host for the virus and the mite vector. Planting roses with adequate spacing and incorporating non-rose plants as physical barriers can help slow the wind-borne spread of the mites. Sanitizing pruning tools after working on any rose is also a good practice to avoid carrying mites to healthy plants.