It is now mid-May, and the lush beds of daffodils and other spring-blooming bulbs have faded into memory. We are waiting for the foliage to turn yellow and die back, so we can clean up our gardens.
Judging from Facebook photos from friends and the flower photos submitted to the Gazette-Journal by Middle Peninsula citizens over the past two weeks, rose season has arrived, and it looks like a splendid one. We Americans love our roses. We prune them, feed and water them, deadhead them, pamper them, and brag about them. We are devastated if one of our beloved roses falls prey to insects or disease.
One disease strikes terror in the hearts of rose growers: rose rosette disease (RRD), also called rose rosette virus (RRV). The interesting history of rose rosette disease begins with the introduction of the fast-growing multiflora rose from eastern Asia in 1866 to use as rootstock to produce other roses. In the 1930s, multiflora rose was planted along banks and railroad lines to prevent erosion; used as a “living fence” to contain livestock, and planted along highway medians to reduce glare from oncoming cars. Multiflora rose spread across North America and became an aggressive, invasive weed that is difficult to eradicate.
Rose rosette disease was first identified in multiflora roses in Wyoming, California, and Manitoba, Canada, in 1941. As multiflora rose continued to spread, so did the disease, a virus carried by the microscopic eriophyid mite, Phyllocoptes fructiphilus. Multiflora roses proved to be highly susceptible to RRD, and the mites, which are carried on wind currents, soon infected roses in home gardens and nurseries. Viral spread also can occur from grafting onto rootstock, with humans as the vector.
Virtually all roses have proved to be susceptible to RRD, including “Knockout” and “Drift” roses, hybrids developed for their profuse blooming, hardiness, and disease resistance. RRD often spreads among rose shrubs planted closely together in hedges or drifts. Virus-carrying mites will migrate from plant to plant.
RRD manifests through a wide variety of symptoms, not all of which will occur on every plant. Common symptoms include rapidly elongating shoots; thick, succulent stems; and small, distorted leaves and deformed flowers. “Witches’ brooms,” which are clusters of new shoots, often appear. The shoots may be deep red in color and “blind,” meaning they will not produce flowers. According to VCE Publication 450-620 “Rose Rosette Disease,” the abundant growth of soft, pliable prickles (thorns) is diagnostic for the disease.
Unfortunately, there is no cure for RRD. Roses infected with RRD can live up to 5 years, but if you discover symptoms, the best course of action is to dig up the entire plant, including all of the roots, and burn it or bag it and get rid of it with your regular trash. Be sure to clean up all leaves and other plant debris. Do not compost infected plants. Remove any roses that are close to the infected plant and disinfect all tools.
The good news is that RRD is species-specific; it only infects roses, so you can plant other species in the spot formerly occupied by the rose. Do not plant another rose in that spot until you can be sure all roots have been removed.
If you suspect that one or more of your roses is displaying symptoms of rose rosette disease, or you would like to be better armed against the possibility of infection, go to roserosette.org, a website partnership between numerous university extension programs, including Virginia Tech, North Carolina State, University of Maryland, University of Delaware, and Clemson University.