Pests and Diseases: Rose Rosette Disease

 

It is with great sadness that I discuss our topic today: Rose Rosette Disease. You see I fear that the glorious Knockout series of roses may follow the same doomed fate as that of the ubiquitous red tips (Photinia). As I’m sure that you’re aware, red tips have been planted ad nauseum in millions of landscapes around the country; when one particular species is planted in such quantity it is referred to as monoculture. When monoculture occurs, it is very easy for a pest or disease to come in and decimate the overplanted plant. In the case of red tips, a fungal leaf spot known as Entomosporium is the culprit. In the case of my beloved Knockout roses, the causal agent is a virus known as Rose Rosette Disease.

WHAT ARE THE SYMPTOMS OF ROSE ROSETTE DISEASE (RRD)?

If you’re like me, when I check Web M.D. or another medical website, I like to skip right to the symptoms to see if they fit my particular ailment so that’s what we’ll do here. By far and away the most tell-tale sign is a witches broom appearance on the new growth. If you’re not familiar with what a witches broom is, the best way I can describe it is it’s like a really compact, version of the plant itself. Here is a picture that is on the Virginia Cooperative Extension website in case my words didn’t do the description justice. Often times the witches broom is bright red in color on the Knockouts and resembles a bouquet of flowers. Another give away symptom is that of excessive thorniness and extremely flexible new growth…so flexible that you can tie a knot in the stem. If you see either or both of these symptoms, you can rest assured that you have the dreaded Rose Rosette Disease.

 

SO WHAT CAUSES ROSE ROSETTE DISEASE?

There is a tiny, microscopic mite that is 1/100 inch long that is known as the eriophyid mite. It is this rinky dinky little arthropod that threatens to remove the Knockout roses from my gardening palette. Notice I said my garden palette, not the garden palette. These mites transmit the virus that cause RRD…now take a guess how they get from one area to another. They blow along in the wind or hop a ride on an unknowing bird or insect. The frustrated part of me thinks “how am I supposed to fight that? Should I put a bubble around the roses or stick them in a vacuum chamber?” Realistically, all you can do is hope that this miserable little mite doesn’t find his way into your garden.

WHAT CAN YOU DO TO LESSEN THE CHANCES OF RRD AFFECTING YOUR ROSES?

  1.  Buy clean stock. Even if you see a killer deal at the end of the season in your garden center, don’t buy it if you see any of the above mentioned symptoms.
  2. Work cleanly. When pruning your roses, sterilize your pruners often and certainly between shrubs. RRD can also be spread by pruning cuts so make sure that you take care not to inoculate your own shrubs with this lethal disease.
  3. Avoid planting cultivated roses near areas that contain the wild multiflora roses. Your approach could be to remove the wild roses as they serve as inoculum for the disease. Or if you know that wild multiflora are in the area, you could avoid planting the Knockouts at all (that thought makes me sad).
  4. If you observe RRD on your plants, you must remove and bag the infected roses. Don’t try to compost them or let them ride in the back of your truck on the way to the landfill…you’ll just be spreading your misery to other gardeners who live along the path to the landfill.
  5. There’s always chemical control but that’s not a philosophy that I really buy into. My theory with plants is that they will either live or die trying. To me, it’s easier to just remove the roses and count your losses.

 

I should note that RRD affects other types of roses but I’m most concerned about the Knockout roses. They are an absolutely delightful plant to cultivate and they reward you many times over what you invest in them. I am as guilty as the 1990’s landscaper who installed red tips at every job. I use them in almost every landscape I design and I realize that I need to curb my enthusiasm so that I don’t add to the monoculture of Knockouts. But it’s a really hard plant to replace…what other shrub blooms from April to December, doesn’t require spraying, and is as beautiful as a rose? If you have any ideas, please e-mail me at stacey@midatlanticgardening.com or leave me a comment below. Happy rose gardening!

December 6, 2011Permalink 16 Comments