Rose rosette disease causes unhealthy, disfigured reddish foliage on infected plants. (Photos courtesy Star Roses and Plants/MCT)
Rose Rosette Disease has been spreading through much of the wild rose population in the Midwestern, Southern and Eastern United States for years, according to research by Chuan Hong, a plant pathologist with Virginia Tech in Blacksburg, Va. Recently, its been confirmed in cultivated roses Knock Out, Drift and Flower Carpet roses, to name a few popular types.
Rose Rosette Disease, first documented in 1941, is traced to the multiflora rose, which came from Japan in 1866 as a common rootstock for ornamental roses. Unfortunately, it was found that multiflora roses are bad because a single plant can produce a million or more viable seeds per plant; over time, the roses have become known as invasive weeds with enormous disease problems. Today, new roses like Knock Out and Drift roses are grown on their own rootstock.
Small mites spread Rose Rosette Disease, and no effective controls are available for existing infected roses. Disease characteristics include witches broom growth, or clustering of small branches, as well as reddening, distorted, stunted and elongated leaves. Infected plants should be destroyed, according to most experts.
Mark Windham, a professor in the entomology and plant pathology department at the University of Tennessee, has done extensive research on Rose Rosette Disease, which he heard about in the early 1990s and now studies through a grant from the American Rose Society. Hes also rose advisor for the Beall Family Rose Garden at the University Tennessee Gardens in Knoxville.
We live with Rose Rosette Disease every day, he says of the gardens 200 plants.
We are constantly vigilant for symptomatic plants. Someone inspects each plant at least five days a week, and any rose that becomes symptomatic is immediately removed and destroyed. Roses next to the diseased rose are tagged and monitored the rest of the season. We lose four to eight plants each year to Rose Rosette Disease.
Even though the short-term future for roses looks scary, Windham is confident the rose industry and researchers will eventually identify sources for breeding resistance into new cultivars. There are no known controls for the virus, he says.
Horticultural oils and Neem oil might help, but there is no data, he says.
The key is constant vigilance for symptoms of the disease and not trying to save any rose that is symptomatic.