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Rose Rosette Disease
Q: I have a group of roses of various kinds in a small flowerbed that has been around for over five years. An unusual thing has happened to one of my rose bushes. This spring, it is growing very small leaves. Really small, like dozens in just a couple of inches of new branch growth. I am hoping this is a genetic thing that could be used to create miniature roses, but I wonder if you can tell me if this is a disease or a problem that isn't a good thing.
A: Unfortunately, it is a problem. I am glad you are on the lookout for potential improvements in your plants, but this is probably Rose Rosette Disease. The symptoms of this disease are variable. We are not even sure if it is caused by a virus, which may mean there is more than one cause for the various symptoms.
Your plants are exhibiting one of the common symptoms of small, distorted growth, often clustered at the end of the branch and called a witch's broom. Some plants get extremely bright red growth, while others grow long stems that have extremely soft thorns that eventually harden. Some plants grow very thick stems that are extremely thorny. If the plant is infected during the summer, the flowers and leaves may become mottled and deformed. All of the plants with symptoms usually die in a year or two, but could live five or more years.
Plants with only a single branch or two of symptoms may go unnoticed for a year or two, but if the whole plant is infected, it is noticeable right away. All infected plants should be destroyed as soon as the symptoms are noticed. Be sure it has Rose Rosette before destroying the plant. Red coloring is often normal in roses, but it tends to turn to green as the growth matures.
Herbicide injury is a possible cause for witche's broom symptoms.
The disease is known to be transmitted by tiny Eriophyid mites, so it is possible that your other plants could be infested if the mites move to the other roses. These mites are resistant to sprays for spider mites. You could use the miticide Avid that is registered for use on both kinds of mites.
Another very important thing to do is to remove any other roses that may have Rose Rosette. Starting back in the 1930's, many Departments of Conservation across the country recommended planting Multiflora rose as erosion control, wildlife food source, living fence for cattle and even as a crash barrier on highways. Unfortunately, it is now listed as a noxious weed in many states. One of the methods suggested to eradicate Multiflora rose was to use Rose Rosette disease. It is highly susceptible, but it doesn't die quickly and the disease can easily spread to roses in the cultivated landscape. There is probably a Multiflora rose source of your disease nearby that needs to be eradicated.
In summary, remove all infected plants, both cultivated and wild. You may want to continue removing Multiflora roses as a benefit to you and the natural landscape. Then, control the mites that transmit the disease. They are more active and damaging on plants in hot dry weather, so using horticultural oils and soaps during the hot dry months can reduce the population to a manageable level.
E-mail questions to Jeff Rugg at firstname.lastname@example.org. To find out more about Jeff Rugg and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.
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