Ask a Master Gardener

photo of rose bush with rose rosette disease

Rose Rosette Disease

1/17/23


My roses were looking kind of funky last year and I am concerned about rose rosette disease. How would I know if they have rose rosette disease? CT

Rose rosette disease is a plant virus that is spread by eriophyid mites. We don’t have a cure and the roses have no natural defense for this virus which usually means the end of your rose bush. But let’s talk about the disease, how to detect it, and what to do about it.

The eriophyid mite is microscopic in size which makes them undetectable to the human eye. They spread the disease by feeding on an infected rose bush and subsequently feeding on a previously healthy rose bush. These mites like to hide in the flower buds, open flowers, or the sepals (the green protective leaves of the bud), among other parts of the plant.

While these mites can crawl short distances, they are typically blown by the wind or transported from bush to bush by your garden gloves, clothing, or tools. Leaf blowers are also considered highly likely to transport mites from bush to bush. Once airborne, they can float some distance to land upon an unsuspecting rose bush. This is especially likely if you have an infected plant located near or amongst other rose bushes. And yes, the mites can ride the air from neighbor’s yard to neighbor’s yard.

There are a couple of main indicators that your rose bush has rose rosette disease. The first thing you may notice is that your rose is growing in an unusual way. By this I mean that new growth is clustered together in a bunch rather that what you are used too. This unusual growth is called a witches broom and the shoots in this growth area tend to be red in color. The second indicator is that you will notice new growth shoots have an abundance of thorns. Yes, roses have thorns, but normally not this many thorns. Once you see it you’ll likely think “I don’t remember seeing that many thorns on a rose bush before.” And you would be correct. It can be an impressive number of thorns.

While these two symptoms are clear indicators of the presence of RRD (rose rosette disease), if you would like confirmation, you can cut off one of the symptomatic shoots, wrap it in dry paper towels, and place it in a sealed plastic bag. Then bring the bag to the the Master Gardener’s office at the Tulsa County OSU Extension on 15th street for positive id. We’ll either confirm it for you or ship it off to the Plant Diagnostic Lab at OSU in Stillwater for a positive id. Sometimes unusual growth patterns can be caused by herbicide drift so it’s always good to get a positive diagnosis.

Since there is no cure for RRD, this typically means that you are going to need to dig up and remove the infected plant from your landscape. If you are not quite emotionally ready to remove the plant, give it a good pruning to remove the symptomatic branches and then wait to see if the symptoms re-appear. Late winter/early spring is a good time to prune if you suspect RRD. In our experience, pruning as a treatment strategy simply delays the inevitable need to dig up and remove the plant.

When removing a plant, you will need to dig up the entire root ball since the virus can reside in the roots as well. Once you dig it up, place it in a trash bag, seal it, and dispose of it in the trash. You will also need to rake up all the leaves and plant debris to dispose as well. After completing this process, clean your tools with a 10% bleach solution and wash your garden clothes and gloves.

The general recommendation is to leave the ground fallow for a couple of months. Rose roots can sprout from root pieces so during this time keep an eye out for new sprouts and remove when found. Mites will die within a few days without a host.

If your infected rose bush in amongst other rose bushes, begin to treat your remaining roses with horticultural oil in an effort to kill any mites that might have migrated to your other rose bushes. You can repeat this treatment each month except during our hot months, then keep on the lookout for symptoms in your other rose bushes. Read the label of your horticultural oil for specific directions.

There are a few things you can do to help minimize the possibility of RRD in your plants. First you can plant with appropriate spacing, separating the roses a bit to minimize the mite’s ability to crawl from plant to plant. Second, plant non-rose plants in between your roses. This will also help minimize direct transfer capabilities. Deadheading roses and disposing of the spent flowers can also help minimize the opportunity for the disease to take hold. And minimize if not eliminate using your leaf blower in the vicinity or your rose bushes.

OSU is conducting tests to try to find a RRD resistant variety of rose, but results are likely years away. See you in the garden!

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org. Photo: Jennifer Olson, Oklahoma State University, Bugwood.org