Rose Rosette Disease

By Kim Willis These articles are copyrighted and may not be copied or used without the permission of the author.

If you grow roses you may have heard of rose rosette disease a deadly viral disease that infects roses.  And if you have been on social media sites related to gardening you may have heard people warning others about Knock Out® roses being the cause of the problem.  That’s a false rumor that should be put to rest.

Knock Out ®roses, are a brand name for a series of easy to grow, hardy landscape roses were introduced to the market less than 2 decades ago.  Rose rosette disease has been around since at least 1940.  While Knock Out® roses are very susceptible to rose rosette disease,(who coined that name?), so are most other roses.   Since Knock Out® roses are very popular and are widely sold throughout North America, they may be the variety of rose that more people see with the problem, but they are not the source of the problem.

It’s perfectly fine to plant Knock Out® roses in your garden, as long as they are healthy plants.  Any rose you plant should be examined for signs of rose rosette disease because any kind of rose could introduce the disease.

The non-native rose, multiflora rose is also cited as the source of rose rosette disease.  Whether the mite that carries the disease was brought in with multiflora roses or brought in later to control that plant is debatable.   It is true that rose rosette disease is very deadly to multiflora roses.  This suggests to me that the disease and the multiflora rose did not originate in the same place as normally if the two co-existed somewhere the rose would have developed immunity.  The idea that multiflora rose is a reservoir for the disease also seems odd.  Something being a reservoir for disease usually means that that plant is able to continue to survive, even if in a weakened state, while carrying the disease.  From what I can read in the scientific literature multiflora rose succumbs to the disease very quickly, usually in the first winter following infection.

There’s no doubt multiflora rose can be invasive and a problem in some areas.  But it was introduced to this country for some of its attributes, it had pretty fragrant blooms that bees love and tiny rose hips loved by birds.  It was used because it spread quickly and formed a thick hedge or ground cover.  And if these roses exist in wild areas near you and they are infected by rose rosette disease the disease could spread to your garden roses.  But the multiflora rose had to get the disease from somewhere; it doesn’t just produce the disease.  Chances are equally good it got the disease from someone’s garden roses as it getting them from other multiflora roses, especially if the disease is new to the area. 

So if your roses get the disease it could have come from nearby wild multiflora roses.  Or it could have come from a rose you recently bought and planted in your garden or from a neighbors rose.  Removing multiflora roses and any native species of rose in wild areas around you might give you a protective barrier if no one else is growing roses near you.

Rose rosette disease
Picture from Clemson University HGIC

Rose rosette disease

Let’s discuss what rose rosette disease looks like and how it’s spread.  The RRD virus is carried from rose to rose in one of several ways.  Tiny mites, not visible to the naked eye are the most common route.  These mites can crawl from rose to rose or worse, because they are so light, blown for long distances on the wind.  They carry the virus in their bodies and transmit to roses when feeding on them, much the way a mosquito carries West Nile virus to humans.  The virus can also be transferred by unsterilized pruning tools from plant to plant.  It can be transmitted during a grafting process, many hybrid roses are grafted on to other roots.  There is some debate on this but some researchers also believe the RRD virus can be transmitted between the roots of nearby roses through root grafting.

Rose rosette disease (RRD) is a viral disease and as a virus, is incurable. It only infects roses.  It causes “witches brooming”, thick multi stemmed clusters of stems, and very red leaves and stems that are thicker and more succulent that other stems.  Caution:  many roses have new foliage that is red, especially in cool weather.  If foliage greens up and looks normal in a few weeks it’s not infected.

The stems infected with RRD are usually covered in tiny soft thorns, which make stems look bristly or hairy.  Some roses get yellowed, distorted leaves that look like pesticide exposure.  The roses are weak and sick looking, and do not bloom well.  The plants lose their winter hardiness and generally die over winter if they make it that far.  Some sickly plants do make it to spring though.

RRD can be tricky to diagnose.  Before ripping out plants I suggest you contact your local Extension office, there is one in nearly every county in the US.  Any local USDA office may also be able to help.  Ask them how to submit a plant sample for diagnoses.   There may be a fee, depending on your state.

While keeping mites off the roses is a good idea, killing the mites with pesticides will not help the problem if the roses are already infected with RRD.  Pesticides, including systemic products, cannot cure the viral disease. 

Most experts recommend you don’t even try to save plants.  If you happened to catch the symptoms quickly it’s theoretically possible to prune off the infected stems well down below the reddened area and halt the progress of the virus.  Then treatment with pesticides for mites might save the plants if they quickly kill them before re-infection occurs.  However trying to keep plants with RRD alive is probably a bad idea since they would become that infamous reservoir of disease.

Rose rosette disease
Kerry Wixted

RRD infected roses should be dug out of the garden, making sure to get all roots.  Plants can then be burned or placed in plastic bags and sealed tightly and removed from the site.  Don’t plant roses in the same spot for a few years, other plants are fine.   If you have other roses without symptoms spray them with pesticides that kill mites, (and this is the time to use conventional pesticides and not organic brews,) and watch them carefully.   Epsom salt, baking soda, beneficial bacteria, milk sprays and so on are absolutely useless for treating RRD.

Prevention of RRD

Examine new plants carefully for signs of RRD.  You may want to avoid dumpster diving for plants; even plants that aren’t roses may have mites on them if roses are sold at that location.  Trying to rescue sickly plants on clearance sale carries a risk also.  Isolate all plants like this away from your garden for several weeks if you decide to do these things.

When you visit other gardens, particularly private ones that have roses, you may want to remove your clothing and shoes and clean them before going into your own garden.  Florist rose bougets probably won’t be a problem, but home grown rose bougets given to you could pose a risk.

Clean pruning shears after pruning each rose; you can keep wet wipe type products in your garden tool bucket for that. Don’t plant roses where they touch each other and using other plants between roses is also a good idea. If roses die, remove all the plant, including the roots.

Many experts recommend several sprays of horticultural oil or insecticidal soap in late spring/early summer.  May and June are the months when mites are most likely to be present in most of the country and these sprays can kill them.  Many rose experts also recommend cutting back roses severely in the spring, 2/3 of each cane, to try and remove any overwintering mites.  In the north this may be too drastic of a pruning if there has been a lot of winter die back.

Keep a close watch on your roses, and have suspected plants diagnosed quickly. Remove infected plants immediately and dispose of them as described previously.  Since wind can bring in mites that carry RRD from long distances even removing wild roses from a huge area around your garden may not prevent the disease.  However if the disease is known to be present in your area removing wild roses might be good move.