Long prized for their striking flowers and wonderful scent, roses are a garden staple in landscapes around the world. But it is not uncommon these days to see rose plants in which something seems off. Gnarled growth, misshapen flowers and large portions of dead tissue are all common symptoms of rose rosette disease, a virus that slowly kills a rose while distorting its growth.
The first infested case in the United States was confirmed in the Rocky Mountains in the 1940s. It was later discovered that the virus infects primarily the multiflora rose, which was brought to North America from Japan with the disease present, according to researchers at Oklahoma State University. As well as being a vector for disease, the multiflora rose is widely considered to be invasive.
Rose rosette disease has spread to rose populations across the continent. The disease is a serious issue in the rose growing industry. In fact, faculty affiliated with the Virginia Tech Cooperative Extension recently declared it one of the most concerning diseases, with most cultivars vulnerable to it. There is no known treatment.
Rose rosette disease (Emaravirus sp.) is spread primarily by two eriophyid mite species, but it can also be spread through grafting. The mites are invisible to the human eye and move from rose to rose mainly by the wind. Once they land on a host, they infect the rose while feeding.
It can take up to four weeks for symptoms to show, usually around the middle of the growing season.
Many of the symptoms are odd. The most common is masses of new growth, predominantly red or sometimes yellow. Rose rosette will also cause unusually long shoots, soft thorns that are more numerous, distorted foliage, swollen stems and dense clusters of congested foliage. Many of these symptoms are mistaken for normal new growth or herbicide damage.
Infected roses will decline until they eventually die. Miticides may be sprayed to slow the outbreak, but most treatments are of limited help because of the size of the mites.
Infected roses should be removed entirely, bagged and disposed of in the trash. This means all parts of the plant — from blossoms to roots and everything in between.
Without a host plant, the mites will die. Since they need the wind to spread, avoid using leaf blowers around roses. Giving roses proper spacing to avoid crowding will help control the mites and mitigate the disease.
When replacing an infected rose, wait at least one or two months, and watch for any root suckers that might pop up. Remove any multiflora rose near other roses, since it is the primary host for the mites.
Only a handful of rose species are believed to be resistant to the disease. Rose breeders are working to create more.
Roses are beautiful and have been a staple in gardening and landscaping for centuries. Despite the threat that rose rosette disease poses, roses can and should continue to be garden mainstays with proper prevention and control.
Wild Green Yonder is a monthly feature from the staff of the Norfolk Botanical Garden, where Tensaie Fesshaye is a rosarian. Send gardening questions to askaplantquestion@nbgs.org.
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Correction. A correction was made on June 11, 2024. Because of incorrect information provided to The Virginian-Pilot and Daily Press, an earlier version of this article carried an incorrect byline. The writer was Tensaie Fesshaye, a rosarian at the garden, not horticulturist Jake Litchfield.
