How to deal with Rose Rosette Disease
By Ann McMillan, Henrico Master Gardener Intern
The horror that is rose rosette disease does not come through in the name.
The word rose carries positive associations from thousands of poems, plays, and love songs. The beauty and fragrance of a rose cannot be improved upon, except perhaps by the latest inspired cultivar. The negatives — thorns, obviously, and the ephemeral nature of the single bloom — only enhance the precious quality of genus Rosa.
A rosette is a ribbon, gathered to resemble a rose, that signifies success or status.
But when rose rosette disease (RRD) takes hold of a rosebush, it manifests as a set of characteristic deformities. One is the witch’s broom cluster of stunted shoots (pictured at right) that, by forming a thoroughly unpleasant rosette, gives the disease its name. Other possible names might have been “unwholesome red streak disease,” “many-more-than-normal-thorns disease,” “weirdly long shoot disease.” The name rose rosette is tidier than the disease itself.
The clincher: no cure exists for rose rosette disease.
Where does RRD come from?
Tiny eriophyid mites (Phyllocoptes fructiphilus Keifer) carry a virus of genus Emaravirus for RRD. This mite and this virus specifically target roses, although other eriophyid mites carry other viruses to other plants. Click here for more information on eriophyid mites.
Despite their lack of wings, these microscopic creatures get around. If an infected rosebush touches a healthy bush, the mites can crawl to their new host. To travel greater distances, they can apparently hitchhike on clothing, gardening equipment, animals, possibly insects — even on a breeze. RRD can move from rosebush to rosebush in a garden, and from garden to garden.
RRD is not picky. All roses are susceptible. The non-native multiflora rose (Rosa multiflora), a quickly spreading thicket of unremarkable white flowers and cat’s-claw thorns, serves as both prey and nursery of virus and mites.
The symptoms of rose rosette disease, according to the Virginia Master Gardener Handbook (2015 edition) are:
- shoots and foliage have an abnormal red color;
- stems appear thick and succulent;
- rapidly elongating shoots;
- shoots with shortened internodes;
- stems with an over-abundance of pliable thorns;
- new growth may have many branches that create a witch’s broom (similar to glyphosate injury);
- distorted or dwarfed leaves (similar to 2,4-D injury);
- deformed buds and flowers;
- abnormal flower color;
- lack of winter hardiness;
- spiral cane growth.
Symptoms are detailed with color photographs in VCE’s Rose Rosette Disease” publication (#450-620, 2012).
There’s no point looking for the mites, since they are microscopic, and only molecular testing can confirm diagnosis of the virus.
Maymont deals with rose rosette disease
A beloved site for weddings — and, not coincidentally, for roses — in the Richmond area is Maymont’s Italian Garden. RRD has dared to strike even there. Sean Proietti, manager of Horticulture and Grounds, says that the disease was first spotted in the Italian Garden in April 2009. (Pictured at left is a rose bush suffering from RRD, provided by Maymont.)
“The horticulture staff realized something was wrong due to the dramatic symptoms of the virus,” Proietti said, “and the disease was correctly identified by the Chesterfield County Extension from a sample. Steps were immediately made to remove the affected roses and control the spread of the disease.
“Initially 90 roses were removed from the Italian Garden in 2009. After extensive research, cultural and tool-sanitation practices were changed. Since then, in a bad year, the horticulture staff may find it on two roses out of the hundred or so roses we cultivate. We bag them and quickly remove them.
“Roses grow quickly, as long as we are taking good care of the roses we replant,” Proietti said. “So we don’t foresee the character of Maymont’s formal gardens changing any time soon.”
What you can do
Descriptions and photographs can help gardeners learn to recognize the disease. Then, look around. “Look closely at roses in commercial shopping center beds,” Proietti said, “it’s really scary how many of those roses are afflicted!”
This knowledge will help home gardeners decide how much risk their existing roses might be exposed to, and whether they want to plant roses in their gardens. Check to see if neighbors’ roses show symptoms. Then widen the search to nearby uncultivated areas that might harbor invasive multiflora roses. “If possible,” says the Virginia Tech Extension publication on RRD, “R. multiflora plants … should be eliminated from the immediate vicinity (100-meter radius) of rose nurseries and gardens.”
By the time the mites are on the rose — long before symptoms appear — the virus is there and will run its course. Virginia Cooperative Extension Pest Management Guide (2022) (PMG) states flatly, “No chemical control [exists] for plant virus disease” (4-10). Roses not yet showing symptoms of disease can be treated with miticides, the proper use of which is detailed in the PMG.
A gardener who suspects RRD can take a sample — thoroughly bagged, of course — to the local Extension office. Once RRD is confirmed, cost-benefit analysis comes into play. One affected rosebush may live and bloom for a year or so after symptoms appear and may be let alone while there is joy to be gotten from it. If the gardener or neighbors have so-far healthy roses, however, the responsible thing to do is to remove the affected bush.
Again, great care should be taken. “First,” Proietti advises, “tie the plant up tight to keep it from brushing on others. Second, throw a heavy-duty trash bag over the plant to keep any mites from shaking off. Third, dig up the plant’s root ball and make sure to get ALL of the roots out. Bag that up as well. If you’re doing it right, your neighbors may suspect you’re disposing of a body. Place ALL the plant material in the trash. Not the compost, not the wood chipper.”
Although RRD does not persist in soil, he continues, “Roses are allelopathic, meaning they suppress the growth of other plants. So, we also recommend removing about two full 5-gallon buckets worth of soil from where the plant was. Lastly, sterilize thoroughly all your tools with rubbing alcohol and replace the removed soil with fresh.”
Last Words on Rose Rosette Disease
Maymont’s Proietti sympathizes with the home gardener affected with RRD. “Losing your first rose to RRD can be pretty scary. But it doesn’t mean you have to give up on roses. I think our experience can show that with a little training and vigilance, you can still have the rose garden you want. RRD isn’t going anywhere, but is easy to identify. And while the treatment might feel a little final, it’s all just a part of life. We replant and move on — you have to if you want your garden to continue to be bountiful.”
Proietti said the other main thing he wanted to convey to gardeners is that they should properly sterilize their pruners with rubbing alcohol between shrubs when pruning.
My personal experience with RRD
In the spring of 2019, a friend and I bought a special-offer three-pack of rosebushes at a buy-in-quantity store. She had a rose garden already established at her home in Northside. I had left some Knock Out roses behind when we moved to a condo. The orange color of the Tropicana hybrid tea rose (Rosa ‘Tropicana’ pictured at right) appealed to me, so it was the one I chose.
Some months later, I asked her how the roses were doing. On the advice of her landscaper, she had torn out the entire rose garden. It seemed that rose rosette disease had begun the sleeper phase of its devastation before she brought in the new roses.
My rose lived for a while, sending up greatly elongated shoots that sometimes bore a gorgeous rose. But by early spring 2022, thorny excrescences covered the red-streaked branches. Its root ball, clubbed and blackened, pulled easily from the ground (pictured at left).
The symptoms were so striking that I took several photos. Then, as the experts advise, I carefully disposed of the bush and the soil underneath. Now I keep a nervous eye on the neighbors’ roses, hoping I won’t have to deliver bad news.
Additional information can be found at https://roserosette.org, a website listing many Extension universities, associations, and commercial nurseries as partners