Rose Rosette Disease
Do your roses have red, distorted, and stunted new leaf growth, or an increased number of shoots (called witches’ brooming), increased thorning, or shortened distances between leaves on stems? How about discoloration, or increased numbers and distortion of flowers? Your roses may have the dreaded rose rosette disease.
There is no cure for this disease right now, and there are no resistant rose varieties. That means your Knock Out roses are at risk. In fact, large mass plantings of any rose variety are often targets for the disease.
Plants that have been diagnosed with rose rosette should be removed from the landscape immediately, roots and all, to prevent the spread of the disease. The diseased plants should be bagged and disposed in the trash.
The widespread presence of multiflora rose in the United States ecosystems has allowed for speedy and extensive spread of the rose rosette disease. Even though multiflora rose is most susceptible, cultivated roses can also be decimated by rose rosette disease. The disease is spread by the microscopic eriophyid mite (Phyllocoptes fructiphilus). The mites transmit the virus that actually causes the disease. They do not fly, but they crawl, ride on passersby, and mostly are carried by the wind.
Be careful when using select symptoms to diagnose rose rosette. When all of the symptoms are present, a diagnosis is fairly certain, but individually, each symptom could be caused by something else. For example, new leaf growth on roses is often red; herbicide (glyphosate) damage causes distorted and stunted leaves and witches’ brooms, and growth regulators (2,4-D) cause increased shoot size.
So take care to prevent infection by removing the oft-infected multiflora roses. Don’t plant downwind from multiflora, provide ample spacing between newly planted roses, and practice good sanitation when pruning. Use of carbaryl spray to control the mites is possible, but it can cause severe outbreaks of other insect infestations.
Rose Rosette Disease, Virginia Cooperative Extension
Frequently Asked Questions About Rose Rosette Virus, Clemson Cooperative Extension