Few rose diseases are more dreaded than rose rosette disease. This disfiguring, deadly pathogen can take a perfectly lovely rose from glory to ruin in just a season or two. It’s very easy to identify, but trickier to manage. Thankfully, there are solutions for ardent rose growers.
Sometimes the best way to learn about a plant disease is to see it for the first time in person. While passing a neighbor’s rose, I noticed it had the most irregular tip growth imaginable. The unusually reddish leaves were dense, fine and the growth reminded me of a stunted witch’s broom (a physiological abnormality caused by various diseases). I took a couple of photos of the strange shoots and leaves, took them home and quickly identified the problem, Rose Rosette Disease (RRD).
This disease, which is caused by a virus spread by a microscopic eriophyid mite (Phyllocoptes fructiphilus), has only been widely troublesome to cultivated roses for the past couple of decades. It was originally found in 1940 on the invasive Eurasian multiflora rose (Rosa multiflora), and to this species it is deadly. But over time it proved itself to be equally as deadly to many garden roses. As with most plant viral diseases, there is no cure for RRD, but steps can be taken to protect your roses. Rose breeders are also hard at work to create RRD-resistant roses and a couple are already available.
Identifying Rose Rosette Disease
Sadly, many favorite garden roses are highly susceptible to RRD, particularly the widely planted Knock Out® roses. Fortunately, it’s a very easy disease to identify. Rose stem tips develop multi-stemmed rosettes with foliage that turns deep red and adopts an almost feathery appearance. Any flowers that bloom from these stems are contorted and small. Stems can also develop excessive thorns, and become elongated and thick. Dieback will eventually occur.
Once a rose has RRD, there is no cure. The best course of action is to immediately remove it and dispose of all parts (far from the garden). Also be sure to sanitize any cutting tools you used in the process. Hand washing them and then spraying them with an anti-viral cleaning spray works.
Protection Against Rose Rosette Disease
Managing Eriophyid Mites: The mites overwinter on stems and dead leaf material, and live on the summer leaves and stems. Here are some ways to keep them away.
- Prune your roses heavily in late winter (remove all clippings)
- Clean all fallen leaf material in fall
- Apply dormant oil spray on plants in late winter
- Apply summer oil spray on plants during the growing months.
Managing Roses: There are several things you can do to help protect your rose plants from infection.
- Space specimen roses apart, to avoid cross-infection
- When you purchase new roses, be sure you buy them from a respected growers that ensure they are RRD free
- Monitor your roses for symptoms
- Keep roses well-pruned and clean fallen leaf material
Managing RRD Roses: If you visit a garden with infected roses or find that one of your roses has symptoms, take caution. The mites can travel on clothing (though they can only survive off of rose plants for 8 hours), so be sure to avoid infected roses. As soon as you have determined you have a rose with RRD, take the following steps.
- Spray nearby plants with summer oil spray
- Remove the diseased plant completely and dispose of it in a trash bag
- Clean the area where the rose was planted
- Plant something new in the spot because RRD will remain in any root tissue remaining in the soil
RRD Resistant Roses
Many species roses are highly resistant to RRD. These include some garden-worthy types, including the European burnet rose (Rosa spinosissima), which boasts single or semi-double white flowers followed by large, near-black hips that appear on spreading bushy plants. The North American the pink Virginia shrub rose (Rosa virginiana) is also reportedly resistant, along with several other pretty American wild roses. (Read more about growing wild American roses here.)
Some lovely hybrid roses are also proving to be remarkably RRD resistant. Of these, the 2018 Weeks Rose introduction Top Gun® was the top RRD survivor in numerous rose rosette disease trials that included hundreds of other rose varieties. The shrubby rose grows to 3′ to 4′ tall, and its flowers are semi-double, burnished red, and moderately fragrant.
Many RRD resources are available at roserosette.org. This organization is dedicated to controlling the disease and encourages early detection and reporting of RRD. It’s the best online resource available for information and help!