A favorite gardening plant has been dealt a huge blow with the onset of a quickly-spreading virus.
The Knockout rose has long established itself as a favorite of homeowners and landscapers alike. Recently, however, the rose rosette virus has reared its ugly head in the CSRA and is leaving lots of rose growers wondering if their plants will be the next to be affected by the disease.
Richmond County Extension Agent Sid Mullis brought the rose rosette virus to the attention of area master gardeners last week when he sent out an email announcing its arrival in the area. A homeowner in Westlake Subdivision in Evans had brought him a cutting of one of her knockout roses earlier in the week and it was confirmed to be rose rosette virus.
“Just last April I had a master gardener forward me an article about rose rosette virus asking what was up with this,” said Mullis. “I told him that I hated to hear about the problem on Knockout roses and had not had anyone call me about it yet, but it sounded like it was only a matter of time before we get it in the Augusta area.”
The virus, according to research done by Mullis, is spread by the ‘rose leaf curl’ eriophyid mite which is found predominately on multiflora roses. Multiflora roses were introduced to the eastern U.S. in the 1800s from Japan. They grow wild in many places and are considered invasive/noxious weeds.
“The wild multiflora roses were thought to be how the mite and virus spread into rose landscape plantings,” said Mullis. “Since Knockout roses have been so disease resistant, they just blanket commercial and residential landscapes throughout the south. The presence of all these Knockouts provides an easy means for the mite and virus to spread from plant to plant and location to location.”
The rise in the number of Knockouts affected by rose rosette has led to the speculation that the virus is likely spreading through nurseries as well, according to one expert.
“Dr. Jean Woodward, Extension plant pathologist, confirms her suspicion that some plants are already infected when they are bought at the garden center because she has seen intermittent problems in beds with several plants,” said Mullis.
Woodward’s theory is that, “if the problem came from the wild roses, it would start at one end and work its way over to the other plants.”
The only way to control the virus is to rid the landscape of plants that have rose rosette virus. Symptoms are similar to herbicide injury and include an increased and rapid elongation of new growth, abnormal reddish discoloration of shoots and foliage, proliferation of new shoots, an overabundance of thorns and deformed buds and flowers.
Commercial insecticides can provide some control over the spread of the disease from one plant to another, although miticides in local garden centers won’t help with the control. If pruning, be sure to clean equipment between plant prunings.