You are currently here! -
  • Home
  • - Virginia plants - Science Wednesday: Rose Rosette, the Knockout Rose’s Enemy

Science Wednesday: Rose Rosette, the Knockout Rose’s Enemy

If I’ve been to your house you probably know that I’m not a plant disease and pathology expert. Outside of a narrow range of issues I’ve personally dealt with, the best I can do is look at, say “yep, that looks bad,” and give you someone to call.


Last year, at an estate property I designed, I was doing an inspection walk with the owner and James from Bartlett Tree. We noticed that the Knockout Roses had whole sections that looked shriveled and contorted. The owner and I were baffled, but James knew immediately what it was.

Rose Rosette Disease

Rose Rosette Disease is nasty, you guys. From the University of Kentucky Cooperative Extension’s fact sheet on Rose Rosette Disease, here are the symptoms:

  •  Increased growth/rapid elongation of shoots
  • Abnormal red discoloration of shoots and foliage
  • Witches broom (prolific clustering of small shoots)
  • Spiral pattern of cane growth
  • Shortening of internodes (shorter stem length between leaves)
  • Distorted or dwarfed leaves
  • Overabundance of thorns
  • Atypical flower coloration (e.g. mottling of otherwise solid-colored roses)
  • Deformed buds and flowers
  • Increased susceptibility to other diseases, such as powdery mildew
  • Lack of winter hardiness
image credit: Missouri Botanical Garden (click to visit)
image credit: Missouri Botanical Garden (click to visit)

What’s amazing is that this is a disease that’s hammering all roses, including the multiflora “weed” roses, Knockout Roses, and the fancy heirloom roses. It’s nasty stuff.

What causes Rose Rosette?

Scientists have figured out that Rose Rosette is caused by a virus that’s carried by a mite or transferred via grafting. These mites are so small you’ll never see them without a microscope. They don’t fly, but they can crawl from plant to plant if your rosebushes touch. They can also drift on air currents or hitch a ride on other insects.

Image credit: THE Ohio State University (go Buckeyes!)
Image credit: THE Ohio State University (go Buckeyes!)

How do we treat Rose Rosette?

Once your rose is infected, it has it. There’s no treatment program for it, and UK Extension folks recommend

Infected plants, including roots, must be removed completely, Diseased plants should be immediately bagged and removed from the vicinity so that the pathogen is not spread to healthy plants. Alternatively, where permitted, infected plants may be destroyed by burning.

That sounds pretty dire, right? And while the virus doesn’t live in the soil, it can remain in roots or plant tissue that’s left behind. It’s essential that you remove everything if you want to keep roses on property. While one of my clients states that he prevented infection of new roses by burning the soil with a blowtorch after removing the infected roses… this is the same client who swears that his wisteria started blooming because he went outside buck naked under a full moon and beat the hell out of the plant with a broom. Follow such anecdotal advice at your discretion/risk.

So, no more roses?

I don’t think that’s the case. Yes, it’s a nasty disease for which there is no cure. But getting your roses from a reputable grower with good sanitation practices can be a good step to keeping the disease off your property. Planting roses so they don’t touch other roses is a current recommendation, as is staying at least 100 yards from multiflora or wild roses, as they seem to be one of the major avenues of infection. There are also other recommendations on UK’s fact sheet.

Last but not least, make full use of your local county extension agent! If you live in Virginia, here’s a link to all the local extension offices. You will not meet a smarter, more helpful group of folks. I met this summer’s college interns for the Fairfax office and I told them straight up, “I hate you because I am SO JEALOUS that you get to intern there.” Super awesome folks and it’s a great taxpayer-supported resource that no one knows about. Give them a call, they’d love to answer your questions!


Virginia Cooperative Extension & Fairfax County Master Gardeners Notes from the Lab, Week 6-7, July 11-July 25 2015

University of Kentucky Cooperative Extension Service Plant Pathology Fact Sheet, Rose Rosette Disease, Nicole A. Ward & Cheryl A. Kaiser, issue May 2012

leave a comment