Dear Miss Floribunda,
They’re ba-ack! Last week I found severe signs of rose rosette disease on my Carefree Beauty rosebush, with contorted leaves and reddish sprouts shooting out of other sprouts. I remembered seeing it on a friend’s rosebush in Hyattsville a few years ago, and she wrote you about it. Because you said that a rosebush with RRD was like the beloved dog in “Old Yeller” who became rabid and had to be destroyed, I cried a little and then got my son to dig up my own favorite rosebush. He knew it shouldn’t be composted, so he bagged it in plastic and it went out with the garbage. Now I hear there is an outbreak in College Park, which isn’t far away. You have written twice before about the seriousness of this disease and its history, but what I’d like to know is whether or not there has been any progress in prevention and treatment. I think the reason it doesn’t go away is that few people are willing to dig up a rosebush and throw it away. They probably just prune it and hope for the best.
No Longer Carefree on [name withheld to prevent panic] Street
Dear No Longer Carefree,
The irony is painful, but Carefree Beauty and many otherwise low-maintenance roses are the most susceptible to RRD, or rose rosette disease. It’s a virus carried by a microscopic wingless mite (Phyllocoptes fructiphilus) that was introduced into the U.S. by the U.S. Department of Agriculture in the 1930s to control invasive multiflora roses. Carefree Beauty and other open-flowered shrub roses are similar to this otherwise indestructible rose variety. Again we run into the law of unintended consequences. The multiflora rose, which is quite lovely, was imported into the U.S. from Asia in the 1860s for use as rootstock and as a fence around pastures. It soon invaded pastures and even forests, creating a thorny mess that prevented grazing and eliminating native species wherever it spread. The RRD virus was effective and wasn’t supposed to affect any other rose, but it obviously has — sometimes in epidemic proportions.
My cousin Moribunda, an expert on such dread diseases, affirms that afflicted rose bushes live only two or three more years after being infected, even though they may continue to flower. She is aware that some experts claim that pruning the canes down to the ground and destroying the canes is sufficient to stop the spread of the disease and to allow the plant to recover. She vehemently disagrees. She even advises you not to plant another rosebush in the site of the diseased one for at least two years for fear of infection from the soil.
I decided to consult Citizen Cane, who is every bit as knowledgeable but not as pessimistic as my cousin. While he agrees that you should destroy rather than cut back a rose afflicted with RRD, he believes that progress is being made against the disease. Rose growers are endeavoring to develop roses resistant to RRD while experiments are being made in the use of other predatory mites to turn the tables on the RRD mite. So far, the Amblyseius fallacis mite has been most promising, at least in controlling mites prevalent in greenhouses. Again, we need to wait and see.
In the meantime, Dr. Cane changed some advice he had given me in the past. Years ago, he advised me to apply Avid, a powerful miticide, on my rose bushes in the spring. Because Avid was prohibitively expensive, I just took my chances, and when one of my “carefree” shrub roses did show the witch’s broom characteristic of RRD, I ruthlessly dug it up and replaced it with a hydrangea. Dr. Cane now tells me that Avid is useless and that he has switched to spraying a light horticultural oil in the spring as a preventative. He tells me that a mite attack is most likely in spring on early growth. Frequent rain also abets it. Dr. Cane had another piece of advice. Chemical pesticides can blow into your yard and cause a certain amount of distortion of new growth on your roses. Alarmed gardeners should wait a bit to be sure the twisted and thorny witch’s broom, with its red-veined leaves, has developed before digging up any roses. The damage caused by the pesticides should go away. RRD damage gets even uglier.