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ASK THE EXPERTS

Rose rosette disease

POSTED: June 19, 2013 4:00 a.m.

Rose rosette disease is a viral disease that is becoming increasingly more common in Georgia.

Extension agents throughout the state seem to be receiving more samples of RRD-infected roses. The disease is spread from plant to plant by tiny eriophyid mites. RRD only affects roses, and it is thought that most species and cultivars are susceptible.

The disease was first discovered in the 1940s. Over the years, the eriophyid mite was known to be the transmitting agent, but the disease-causing agent was a mystery. Only in 2011 was RRD found to be caused by a virus.

Disease symptoms can vary depending on the species and cultivar of rose. According to Alabama Extension Pathologist Jim Jacobi, the most common symptoms include: ‘witch's brooms' or abnormal clustering of small branches, distorted leaf growth, reddening of leaves, rapid stem elongation, stems that are thicker than parent stems, and excessive thorn production, with the thorns being very pliable, and red or green in color.

RRD can be difficult to diagnose because it mirrors some symptoms of herbicide damage from chemicals like glyphosate (Roundup) and 2,4-D.

The disease is known to be harbored on multiflora roses. These were introduced to the eastern United States in the 1800s from Japan and are now considered invasive. They have leaves with 5-11 leaflets, white flowers and bare red fruit. They can often be found in woodlands surrounding home sites.

Unfortunately, there is no cure for roses infected with rose rosette disease.

Infected rose bushes, including roots, should be pulled up and removed. You can either burn the infected plants or bag them up and put them in the trash.

If you notice any multiflora roses growing wild near your house, remove these plants if possible. Again, they are invasive and serve as the wild host for RRD.

After removing infected plants, surrounding plants may be treated to help reduce mite populations which spread RRD. An insecticide such as bifenthrin should help control mites. However, eriophyid mites are small, so complete leaf coverage of sprays is essential. Also, most bifenthrin label directions call for application every two weeks from April to October. This just isn't practical for most homeowners.

There is currently research being conducted at several universities in order to find potential RRD-resistant roses. Because scientists have isolated the virus responsible for RRD, quick-test kits will hopefully become available in future years for positive identification on-site.

If you think you have a rose bush infected by the disease, bring in a sample to the office or send me some photos via e-mail. Early identification and plant removal can be the difference between losing one or all of your roses.

Clark MacAllister is the Dawson County extension agent. For more information, call (706) 265-2442.

 

 

 

 

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