Dear Miss Floribunda,
Several of my rose bushes have gotten RRD (Rose Rosette Disease), and I have dug them up and put them in black plastic bags for trash pickup just as you’ve previously advised. I’m worried that I have recognized its tell-tale thorny witch’s broom distortions on rose bushes in other gardens throughout Hyattsville and Riverdale Park. I have left notes of warning at homes where I’ve seen the diseased bushes, but nothing has been done. I worry that there could be a real epidemic, and my own garden could be decimated. I just don’t know what more to do.
Perhaps you can again warn people how serious it is to ignore the signs of this disease. Also, do you know if any progress has been made towards discovering a cure?
On the Thorns of a Dilemma on Decatur Street
Dear On the Thorns,
First the good news: The Potomac Rose Society (PRS) has on its website (potomacrose.org/Rose-Care) both a flyer and a detailed letter you can download, print and distribute. Thanks to the prestige of the PRS logo, the flyer might be more effective than a handwritten note from a stranger, and the letter would give both explanation and instruction.
Now for the bad news: Although assiduous research is ongoing, there is still no effective cure for RRD, or Rose Rosette Disease. It’s a virus (Emaravirus rosae) carried by a microscopic eriophyid mite (Phyllocoptes fructiphilus), introduced into the country by the U.S. Department of Agriculture (USDA) in the 1930s to control invasive multiflora roses. As happened when the ultimately invasive kudzu was introduced to the South by the Soil Conservation Service in the 1930s to control erosion and add nitrogen to the soil, we’ve run into the law of unintended consequences.
The multiflora rose was imported into the U.S. from Asia in the 1860s for use as a root stock and as a fence around pastures. It soon invaded pastures and even forests, creating a thorny mess that prevented grazing, while also eliminating native species wherever it spread.
The RRD virus was effective in destroying the multiflora rose, and wasn’t supposed to affect any other rose — but, of course, it most certainly does. Because the RRD virus’s vector is wind-borne, by 1994 rose bushes on the East Coast and as far south as Tennessee were its victims.
My Cousin Moribunda, whose obsession is plant pathology, affirms that afflicted rose bushes live only a few years after being infected, though they may continue to flower. She is aware that some experts, such as my friend in the American Rose Society, Citizen Cane, believe that pruning the canes down to the ground and destroying them is sufficient to stop the spread of the disease and to allow the plant to recover. Moribunda very much disagrees. She even advises you not to plant another rose bush in the site of the diseased one for at least two years, for fear of infection from the soil.
I notice that the PRS letter referred to earlier, however, refutes this opinion, while giving instructions for disposing of the bush rather than composting it. Personally, I think it is simply prudent to wait a year or so before replanting with another rose. To guard against developing a monoculture that invites disease, you might replace it with one of many companion plants that benefit roses.
I asked Citizen Cane (whom I consider as knowledgeable, but not as pessimistic, as my cousin) for a progress report on RRD prevention or cures. He told me of a number of active research programs — the earliest begun by the University of Tennessee in the 1990s, later joined by the Texas A&M AgriLife Extension Service, with funding from the American Rose Association.
The USDA Specialty Crop Research Initiative funds the resolutely diligent Sustainable Roses project, which was established following the industry-wide Rose Rosette Summit of 2013, organized by Star Roses and Plants and the Garden Rose Council.
Scientists are not only trying to find cures but also to develop roses resistant to the disease. Intensive study has begun of our own native roses, which are immune to, or only mildly affected by, the disease, and cross-breeding may result in some wonderful new roses.
Our native roses are very lovely, though their blooming season is short, and they come only in various shades of pink and white. Personally, I treasure my Virginia rose (Rosa virginiana) because of its sweet fragrance, and my swamp rose (Rosa palustris) because it thrives in shade — something remarkable in a rose.
Other native roses include the Carolina rose (Rosa carolina), which is notably fragrant; the early wild rose (Rosa blanda), which is thornless; and the Woods’ rose (Rosa woodsii), which has attractive red hips in fall.
In the past, Citizen Cane advised applying miticides to rose bushes in the spring, but now he admits they are ineffective and has switched to spraying a light horticultural oil on his rose bushes in March as a preventative. He tells me that RRD attacks are most likely in spring on early growth. Frequent rain also abets the virus.
Citizen Cane also notes that chemical pesticides can blow into your yard and cause a certain amount of distortion of new growth on your roses that mimics RRD. Alarmed gardeners should wait a bit to be sure that the twisted and thorny “witch’s broom,” with its red-veined leaves, has developed. Any damage caused by pesticides should go away, while RRD damage gets even uglier.
To discuss this and other gardening concerns, perhaps you’d like to come to the next meeting of the Hyattsville Horticultural Society on Saturday, July 19 at 10 a.m. in the multipurpose room of the city municipal building (4310 Gallatin Street).