If you grow roses you may have heard of a deadly disease called Rose Rosette, or “witch’s broom”. If you haven’t, then now is the time to learn about it, especially if you have Knock Out® roses, or any kind of rose, in your landscape. It is mistakenly thought that this disease only affects Knock Out® roses; however the high infection rate in these roses is most likely due to them being planted in huge numbers across the Metroplex. Rose Rosette can infect any rose variety in your landscape.
How do roses contract Rose Rosette Disease
This devastating disease is transmitted by a tiny mite called Phyllocoptes fructiphilus. The disease infects only plants within the genus Rosa, which includes all roses. It can spread quickly from plant to plant via the mites.
Signs to watch out for include:
The most noticeable sign of Rose Rosette is when the stems grow into a shape called “witch’s broom”. A multitude of stems growing en masse with dense clusters of thorns. Unfortunately, this appearance can also be produced by drift from broadleaf weed killer and sometimes the two are confused. If you notice the “witch’s broom” growth plus any other symptoms, but you’re not confident the disease is present, it’s best to call a professional for a correct diagnosis.
How fast does it kill?
Rose Rosette Disease can take up to two years to kill your rose plant. This slow-death is often what causes homeowners to think they may have cured their plant. But in that time, the mite that causes it will have most likely spread the virus to other roses in your landscape, your neighbor’s landscape, or all over your neighborhood. Because the disease is a virus, or virus-like, there is currently no cure.
The best treatment is to completely remove and destroy the infected rose plant, including its root system, as soon as you see signs. Do not put infected plants into the compost pile! Place them directly into the trash so that mites do not spread.
Are there treatment options?
While commercial growers do have access to several miticides that can be used against the mites during production, options for landscape control are limited. Unfortunately, the systemic miticides available to homeowners for landscape use are not effective against the mites that transmit rose rosette. It is thought that preventative early spring and summer treatments on uninfected plants with insecticidal soaps, horticultural oils or other natural miticides could help protect them from infection. However, because the mites are so small it can be difficult to ensure that these treatments will prevent mite infestation.
It is also thought that strategically pruning out infected canes can stop the spread of the disease and save your plants. However infected canes may not show signs of the disease for many months, which means they could still host the virus that the mites could continue to spread. Therefore, pruning has not yet been proven an effective treatment.
Again, the best control for this disease is to remove infected plants completely, including the entire root system. Remove all fallen rose leaves and other leaf litter underneath the plants, where mites can take refuge.
So you’ve pulled out all your infected roses…can you plant new roses?
It’s not advisable to plant new roses into the same area for at least a year or two. Even small pieces of infected root system accidently left behind in the soil can produce new infected shoots. Mites can then begin spreading the virus again from these shoots. Plus, if your neighbor's roses have the disease, it’s only a matter of time before it will most likely be transmitted back to your new roses.
When purchasing new rose plants be sure to inspect them for signs of the disease before you buy them.
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