For those of us with an emotional attachment to our roses, nothing is more devastating than Rose Rosette Disease (RRD). Rose Rosette Disease is awful because there is no cure – when this virus hits, there’s no way to save your plants.
There are a host of other issues that can affect your roses, of course, but RRD – which was first discovered in American gardens in the 1940s – is one of the worst.
This disease, also known as “witch’s broom” appears on every variety of rose and can spread rapidly throughout your rose garden. But what is Rose Rosette Disease and – most importantly – how can you prevent it?
What is Rose Rosette Disease?
Roses bring out a lot of emotions in some gardeners. In my garden, many of the roses are descended from my grandfather’s plants. Whenever I see them, I think of his tiny yard.
It had a pretty, postage-stamp lawn with a tall pear tree in one corner and yew bushes along the edges. But half the yard was devoted to my grandfather’s roses. In the summer, we’d sit on the back steps and breath in the scent of blossoming flowers.
That’s why we try to divide up our emotionally important roses by spreading them out among family members in various states. If my sister in the south loses her roses, I can bring her cuttings from New England.
How Does This Disease Spread?
Rose Rosette Disease is caused by the Rose Rosette Virus – a virulent pathogen spread by tiny, eriophyid mites. The mites themselves are so small that they can’t be seen by the naked eye. To see them, you’d need a strong magnifying lens.
Eriophyid mites can’t fly, but they’re so tiny that they’re often carried by the wind from garden to garden. These mites feed on roses of all species. If the eriophyid mites feed on an infected rose plant and then move to a healthy garden, they transmit the virus as they feed on healthy roses.
Because the mites that spread RRD rely on the wind to carry them from rose to rose, cases of Rose Rosette Disease tend to be clustered. We don’t know much about this disease or the mites that spread it yet, but there are no reported cases in areas with extreme winters.
Northern Idaho and upstate New York are the areas with the harshest winters where this disease can be found.
Northern New England, Alaska, the Dakotas, Oregon, and Montana have not reported any cases of RRD. Colorado and Hawaii also have no reported cases. Northern Minnesota, Wisconsin, the Upper Peninsula of Michigan, northern Nevada, and northern Arizona are also currently free of RRD.
Perhaps the mites who spread Rose Rosette Virus can’t survive in these challenging climates. We don’t know for sure, but researchers are hopeful that there may be limits to the spread of RRD.
Recognizing Rose Rosette Disease
RRD is called witch’s broom for a reason. One of the most telling signs of Rose Rosette Disease is the initial vigorous and clustered growth of the rose canes. These bunching canes grow quickly, but they tend to look frazzled and ragged.
The new growth is reddish in color – like new growth is in a lot of rose cultivars. But unlike healthy roses, the rosy hue never matures to green. Then, the bunchy, new growth starts to put out clusters of “rosettes.” These rosebuds rarely open, if they do bloom, the flowers are stunted and deformed.
The stems of roses affected by RRD grow thick, red, and extra thorny. Plants might have one of these symptoms, a few of them, all of them, or no symptoms at all.
Rose Rosette Disease is fatal, your rose plants won’t survive the virus for long. It causes plants to become weak and to fail.
If you’re not sure whether it’s a true RRD infection, reach out to the USDA for confirmation. Sometimes, herbicides can cause similar damage to Rose Rosette Disease. If there’s a chance that an herbicide has caused the damage, watch for lots of vigorous growth. Only Rose Rosette Disease causes such a quick growth of damaged canes.
Since there’s no chance to wait out this disease or heal your plants, it’s important to remove infected roses as soon as possible. The longer infected plants stay in your garden, the more likely it is that the disease will spread. It’s also important to report your cases of RRD to the USDA.
So much research is still being done on RRD – your case could help. Reporting can also help you – RRD researchers can give you up-to-date advice on how to reduce the spread of the virus and save your remaining roses.
Dealing with Infected Plants
Rarely, if you catch it in time, pruning infected canes might limit the spread of RRD. The virus is systemic and usually flows throughout the plant, even if you don’t see evidence of it.
At the first sign of infection, prune and dispose of the affected canes. If you see more signs of Rosette Disease after pruning, dispose of the entire plant.
Most of us keep trying to prune away the infection until the entire plant is affected. All this does is give the Eriophyid mites an opportunity to infect other roses. If the disease is continuing to manifest, destroy the plant.
Then, avoid planting roses in that area for at least a year. Eriophyid mites can’t overwinter in the soil, but since we don’t know a lot about this disease it’s best to play it safe.
Preventing Rose Rosette Disease
There may not be a cure for RRD, but there are a lot of ways to reduce the chances of losing your beloved roses to this virus. One of the best ways to prevent the spread of RRD is pruning.
In the fall, prune your roses and dispose of the pruned sections. Eriophyid mites overwinter on unpruned rose plants, so don’t give them that opportunity.
Continually deadheading your rose plants denies the mites an opportunity to gather around dead blossoms. Deadheading and fall pruning are the first steps in preventing RRD. Of course, they can’t guarantee that your roses won’t catch Witch’s Broom, but proper pruning and deadheading will reduce the likelihood.
What About Row Covers?
While the idea of rose row covers seems like a good idea to keep mites away, row covers actually do very little to protect from mites. Eriophyid mites are microscopic. They can fit through row covers. The microscopic size of these pests makes it hard to use conventional protective measures against them.
But, while row covers rarely work, windbreaks can help. Building or planting barriers between your roses and the wind will reduce the number of mites blown onto the roses. One of the best ways to reduce the chances of RRD in your garden is by protecting your roses from the wind. Plant non-mite hosting bushes between rose plants, use barrier walls, or wooden plant protectors.
It’s also important to avoid creating your own wind around rose plants. Don’t use leaf blowers or fans in your rose garden. Anything that creates a bit of wind is helping the mites find their way onto your roses.
Space Out Your Roses
Since Eriophyid mites can’t fly, proper plant spacing can help reduce the damage caused by RRD. Rose Rosette Disease is only transferred by Eriophyid mites. You can’t spread it with pruning shears, and the virus can’t live in the soil.
So make sure your rose plants are touching each other. Plant non-host plants in between roses and give each plant a little extra space. Proper plant spacing can stop RRD from spreading. Even if the disease affects one of your roses, you can keep it from infecting all of your roses.
If you have wild roses nearby, and you’re concerned about Rose Rosette Disease in the area as well, remove the wild roses. Wild roses are beautiful, but they’re also an ideal host plant for Eriophyid mites. Wild roses can be infected for a long time and act as a host plant for mites as they wait for a stray gust of wind to send them into your garden.
If RRD is spreading in your area and wild roses are too, get rid of them both to keep your garden roses safe.
What About Miticides?
Unfortunately, miticides are not effective against Eriophyid mites. Consistent applications of horticultural oil might help slow the spread of RRD a bit, but they’re only moderately effective against these mites.
If you’ve just removed an infected rose from your garden, definitely give horticultural oil a try. It may save some of the other roses. But don’t expect it to wipe out the mites entirely.
Resistant Rose Varieties?
At this point, there are no rose cultivars that are resistant to RRD. Gardeners are hoping to change that in the near future, but for now, there aren’t any plants on the market that can stand up to the Rose Rosette Virus.