What Is Witches' Broom?
By: Randy Forst
Rose enthusiasts—BEWARE! There are more than just ghouls and goblins to watch out for in your garden. Keep an eye on your prized blooms because witches’ broom may be in your flowerbeds!
Witches’ broom is a common issue found in gardens. These spooky brooms aren’t flying or sweeping, however. Witches’ broom is a clear sign that your plant is having issues and needs your attention. Master Gardeners and home gardeners alike need to know how to spot this eerie phenomenon in order to best care for their plants.
In this article, you can learn what witches’ broom is, what causes it, how to know
if you have it, and what to do to prevent it.
Witches’ broom is a growth found on many types of plants, commonly on roses, in which a stem branches off into a bundle of offshoots, often appearing like a broom or bird’s nest. This deformity is often a symptom of a disease.
This article will primarily be discussing witches’ broom on roses, but this issue can also be found on many other plants, such as cedar, juniper, mistletoe, blueberry bushes, and oak.
In appearance, witches’ broom can be spotted by its dense and spiky, short stems all shooting off from a singular branch. The condition gets its name from the way it looks: like a broom. Witches’ broom on roses is also known as “rosette.”
Witches’ broom can be caused by many different factors, such as herbicide damage, rust, environmental factors, or even the plant’s genetics. For roses, witches’ broom is often a sign of a deeper and more concerning issue—rose rosette disease.
Rose rosette disease (RRD) is only found in various types of roses. In addition to several offshoots sprouting from a single stem (witches’ broom), in roses, the leaves will change to red, yellow, or reddish brown, and the stem will have an overgrowth of thorns. You may also see elongated shoots from your rosebush, underdeveloped leaves, or discolored or poorly formed flowers. A rosebush with a severe case of RRD may not produce flowers at all.
Many roses naturally have red-colored leaves, and the red color is not the sole indicator of RRD and should not be confused. If you have concerns about your roses, you can send a sample to our Plant Health Clinic.
There is no cure for the disease, and if your roses have RRD, they should be destroyed to prevent further spread.
RRD is caused by the rose rosette virus, a discovery made by University of Arkansas plant pathologist I.E. Tzanetakis and graduate student Alma Laney in 2011! This virus is carried and transmitted by mites, and while the disease is incurable, there are measures we can take to reduce the chances of our roses getting RRD.
It can be helpful to understand how the virus travels in order to prevent the spread of it. The virus, like all viruses, requires a living host. An eriophyid mite (Phyllocoptes fructiphilus) feeds off an infected plant and picks up the virus. It then travels to another plant to feed and transmits the virus to the new plant.
These microscopic mites like to hide in buds, flowers, under leaf scars, and at the base of shoots. While they cannot travel far by themselves, they can be carried by wind, gloves, and tools. The virus can also be transmitted through grafting.
These mites can live through the winter, and you may not see signs of the disease while the infected plant is dormant, but you will see signs once the plant begins producing new growth in the spring.
To prevent rose rosette disease, it is important that you first start with healthy plants, spacing them in such a way that the virus is less likely to spread, and regularly checking and removing diseased plants from the property.
When buying roses, it is important to be critical of the nursery you are buying from. Be sure the seller is reputable, and do not buy plants that look diseased. Healthy roses are going to have plump canes, smooth bark, and feel a bit denser or heavier, as this is a sign that the canes are full of water. Unhealthy plants will be brittle, dried out, and weak.
If you are buying roses grown in containers, we recommend investing in larger plants as these tend to be more successful and easier to grow. Large roses should be in 2-gallon containers and small and medium sized roses should be in at least 1-gallon containers, as the roots need plenty of space to grow successfully. Smaller containers are more likely to hinder the growth of the roots.
As you are buying roses, be on the lookout for signs of rose rosette disease as mentioned above, such as witches’ broom, elongated stems, discoloration, and an overgrowth of thorns.
A deal on the price tag may not actually be a plant worth bringing home!
While you are choosing spaces for your roses to go, you will want to avoid placing them too close together. Remember, the mites that carry RRV can blow to other rose plants in the wind, so giving them plenty of space is a good idea.
You may also consider planting non-rose plants between your roses to provide a barrier. Pay attention to which ways the wind typically blows in your garden and consider providing wind barriers, like tall, non-rose plants, trellises, fences, and walls.
Checking on your roses frequently for suspicious activity, growth, or disease is extremely important. We recommend checking your roses about every two weeks during the growing season.
While checking on your roses, look for signs of rose rosette disease as mentioned above, deadhead spent flowers and dispose of the debris in a safe place away from your roses in case they do contain the mites, and perform your typical wellness checks on them.
Do you have rose rosette disease? If RRD is confirmed, immediately remove the infected plant from your yard. If you suspect a rose has RRD, be sure to work with the suspected rose AFTER working with your healthy roses so not to transmit disease to your healthy roses.
💡 TIP: Around February each year, be sure to prune your roses. This can help prevent RRD as well as give you healthier, happier blooms.
We know witches’ broom on roses may seem scary, but with proper care and prevention, your rose garden will be a showstopper! Roses are a beautiful and irreplaceable flower, and proper care will help these beauties thrive. For more information on gardening in Arkansas, check out The Arkansas Garden!
