Rose rosette is a fatal disease of plants in the genus Rosa which is caused by a virus-like pathogen, spread (vectored) by a tiny, eriophyid mite (Phyllocoptes fructiphylus). This mite is so small that it requires 30X magnification to see and is easily dispersed on wind currents. The most common host plant is the noxious weed, Rosa multiflora. However, over the past 10 years, there have been increasing reports of rose rosette infecting domesticated roses. Although there may be differences among rose species and cultivars in susceptibility to this disease, most experts believe that no cultivated roses are highly resistant. Unfortunately, this seems to be true of Knockout® and some of the other low maintenance shrub roses popular in the landscape trade. While they show excellent resistance to black spot, death from rose rosette disease is all too common.
Symptoms of rose rosette disease (RRD) are diverse and bizarre. Initially, the infected plant may have a reddish pigmentation on the leaf veins. Affected shoots may show an abnormally rapid elongation and reddening of the stem and leaves. Gradually, leaves become distorted and there is an abnormal proliferation of shoots and thorns, ultimately leading to a "witches broom" appearance. Shoots often fail to develop winter hardiness and may, consequently, be killed by freezing injury. Flowers that develop on affected shoots are small and distorted. In some cases, damage from glyphosate exposure can create symptoms that look similar to those of RRD.
Unfortunately, there is no cure for RRD. Although infection may start on individual shoots after mite infestation, it becomes systemic, usually causing death of small plants within one or two years. It may be possible to reduce the probability of mite infestation by making weekly applications of pesticides such as carbaryl, horticultural oil or insecticidal soap in May, June and July. Repeated application of carbaryl often leads to outbreaks of spider mites due to elimination of mite predators. Avid is labeled for control of both eriophyid and spider mites on roses. However, the first step in management of RRD should be to remove all multiflora or other wild roses within 100 yards (especially upwind) of uninfected domestic roses. Symptoms of new infections generally start to appear in mid July. Pruning out symptomatic shoots may slow the progression of the disease. However, if there are many uninfected roses in the vicinity, the safest approach is to remove and destroy plants (including roots) that show any symptoms.
RRD symptoms: Reddish foliage and stems and excessive elongation, branching and thorns.
REVISED: September 29, 2015