Thank you to Paul Zimmerman for his contributions to this article.
If you’ve been on some of the rose forums, attended rose talks or even just talked roses on Facebook, you’ve likely heard the term Rose Rosette Disease or RRD. While it’s been around a while, it’s starting to show up on the radar screen of more and more general gardeners. So we’ve decided that it’s time to talk about it.
First, what is Rose Rosette Disease? It is a disease that is carried by a specific spider mite, ‘Phyllocoptes fructiphilus’. An infected mite drifts on the wind, comes into your garden, lands on your roses and then injects the disease into the rose when it starts to feed. Or a non-infected mite can land on a rose that already has it, pick up and then when the wind blows it to another rose, it infects that one.
You know you’ve got it when your roses start to throw off strange growth that is purplish in color and most noticeably has “foliage” in the shape of what is called “witches broom”. It actually looks a lot like damage from a weed killer.
It is particularly lethal to the species rose R. multiflora and in fact has been mentioned as a potential biological control method for it. R. multiflora spreads like crazy, and in much of the eastern United States it’s classified as a noxious weed. Some government officials in their attempt to control it actually facilitated the spread of RRD by purposely infecting stands of multiflora. They claim there was no specific proof RRD infected ornamental roses – the kind you grow in your garden.
Well guess what – they were flat out wrong! It does affect ornamental roses, some more than others. Now that we know what RRD is and how it got here, we can talk about what to do about it.
First off, let’s talk about what you can do to reduce the likelihood of it getting into your garden. Since it hits R. multiflora quickly, check in your area for strands of it. R. multiflora only blooms in spring with smaller white flowers that have about 5 petals each. That’s the easiest time to spot it. When it’s not in bloom the foliage helps. It’s a shiny green and the leaves are elongated and usually thorn-less. It’s a rambler so it throws off long canes. The first step is to dig it up and get rid of it.
If rose rosette does happen to infect a rose in your garden there is no known “cure”. However, we’ve noticed in dealing with it that there are steps you can take. The first is to understand how it spreads in your rose. The mites land on the top of a rose cane where the new tender foliage is. They inject RRD into that part of the rose and from there it slowly travels down through the cane to the base and then up the other canes. The important word here is slowly.
The symptoms on the infected cane (the witches broom) very often show up before the rest of the plant is infected. When you see the witches broom is infected, follow that cane to the base of the plant and cut it off at the base. Put it in a garbage bag and get rid of it so you don’t accidentally shake of any mites onto another rose. This may save the rose depending on whether or not the other canes have been infected already. Eventually, the cut off cane is replaced by a new one as if nothing ever happened.
However, if the disease appears to have spread to another section of the rose you have no choice but to dig the entire rose up and either destroy it or dispose of it in a garbage bag. So does this mean you should stop growing roses? Of course not! Rose rosette disease is a bummer when and if you get it, but by knowing how to deal with it you can reduce it to another part of your normal garden maintenance.
Jackson and Perkins is proud to be a part of the National Clean Plant Network. To learn more about this organization, visit here.