Rose Rosette Disease by PJ LaRue Smith
Rose rosette disease (rose witches broom) has been getting more press the last several years in the Dallas/Ft. Worth area due to the increased infection rate noted at several homes and public gardens. This disease is particularly devastating in that (a) there is no cure, (b) infected bushes must be removed/destroyed, and (c) all roots of infected plants must be dug up before replanting roses in the same location.
Symptoms of rose rosette disease include witches broom formation of new growth, twisted flowers and leaves, excessive leaf growth, excessive thorniness, red and/or mottled discoloration, lateral shoot elongation, flattened stems, and enlarged stems. Not all symptoms may be noted on affected plants, and can differ amongst rose types.
What causes the disease? In 2011, a research group from the University of Arkansas reported the detection of a virus, specifically an Emaravirus, in symptomatic roses. They were able to detect this virus in 84 out of 84 symptomatic plants that were tested (Laney et al, 2011). This study also resulted in a genetic (PCR) test to detect the virus. However, the procedure can be tedious and is currently undergoing further modifications to simplify for ease of use.
How does the disease get into, or transfer from, plant to plant? Evidence from mite transmission studies suggest that the eriophyid mite (Phyllocoptes fructiphilus) carry/transmit some disease causing agent from the diseased plant to healthy ones. (There has not been any published study that clearly demonstrates that the eriophyid mite actually carries the rose rosette virus itself, however.)
How do you know that a rose has this virus? Symptomology as described above, once other factors such as herbicide damage (especially products containing 2,4D), abiotic environmental conditions (i.e. sunlight, temperature, wind patterns, precipitation) and damage by other insects have been ruled out. Presence of the eriophyid mite along with the symptoms listed above further substantiate the conclusion of rose rosette disease. Electron microscopy and other molecular tests can detect the virus, but are typically not done in the average home garden.
Can the rose rosette affected plant be left in the garden? Most of the time, this disease will damage the rose plant to the point where it simply dies. However, the infected plant can serve as a virus reservoir for transmission by the eriophyid mites to healthy bushes. So removing/destroying the plant is the best option for further spread of the disease.
What is the best management practice when this disease is discovered in a garden? According to Texas A&M AgriLife Extension Service publication E-PLP-010 (August 15, 2013):
1. Removal of confirmed and/or symptomatic plants early after observation.
2. Treatment of adjacent plants with miticide to reduce probability of transmission by eriophyid mites. (Please note: this will not stop the virus, if it is already in the plant.)
3. Constant monitoring (weekly) for symptoms and rapid action when and if symptoms are observed.
4. If desiring to replant with roses, it is advisable to remove all diseased plant roots from the soil before replanting in same area. (This is a prudent precaution even though it is unlikely that the virus would spread this way.)
Hopefully, this disease will never visit your garden. If you suspect that your roses may have this disease, please contact the Extension Office at 903-455-9885 for further information.