Rose rosette disease, also known as witches’-broom of rose, is caused by a virus that is spread by a very small, mite. The disease is limited to plants in the genus Rosa.
Symptoms and Diagnosis
The earliest symptoms of rose rosette disease include a red pigmentation of the underside of leaf veins followed by sharply increased growth of vegetative shoots, which are typically more succulent than normal and colored in various shades of red. Leaves often become deformed, crinkled, and brittle with yellow mosaics and red pigmentation. As the disease progresses, leaves become very small, petioles are shortened, and most lateral buds grow, producing short, intensely red shoots. Cultivated roses show symptoms of thickened, succulent stems and a proliferation of thorns.
Virus transmission occurs most readily between the months of May through mid-July when plants are making active growth. Symptoms from new infections usually start appearing in mid-July. In general, smaller plants go through the disease stages more quickly than larger plants. Small plants are usually killed in about 2 years, while a large plant may survive for five years in a deteriorated condition.
The American Rose Society Research Endowment Trust identifies Rose Rosette Disease as the greatest threat to the future of commercial and recreational growth, and the enjoyment of roses. In 2012, ARS selected Dr. Mark Windham to head a three-year study about the management of Rose Rosette Disease. The objectives were to determine how rosarians manage the disease in their gardens and identify best practices besides eliminating plants with symptoms.
The Potomac Rose Society together with the U.S National Arboretum will hold a symposium on the status of current research on this disease featuring Dr. Windham. He will not only identify ways to manage the disease but he will also share a list he has developed of roses that homeowners can successfully grow without reliance on chemical control. For registration information please visit The National Arboretum events website.
by Tina Hochberg, Potomac Rose Society member