Roundup or Rosette

Is it Roundup or rosette? Even your plant doctor may not know
COLUMBIA, Mo. –Residue from late-season Roundup application can mimic symptoms of rose rosette, a disease fatal to many rose species, said the coordinator of the University of Missouri Extension Plant Diagnostic Clinic.
No effective control for rose rosette in infected plants has been found and no current laboratory tests can confirm rose rosette disease, said Simeon Wright.
"I usually ask if the person may have sprayed Roundup near the roses late last summer, allowing the herbicide to come into contact with plant leaves," he said. "If they had not, it is likely to be rose rosette."
Rose rosette is thought to be caused by a virus or virus-like pathogen transmitted by an eriophyid mite called Phyllocoptes fructiphylus, or by grafting.
Symptoms vary depending on species and cultivars. Common symptoms include the development of witches’ brooms, which are clusters of small branches with red pigmentation. Canes may develop excessive growth of soft, pliable red or green thorns.
When Roundup drifts onto the leaves, it can work its way to the roots, allowing rosette-like symptoms to appear the following season.
Plants affected by Roundup can survive. "If you have some normal-looking shoots there is a good chance of recovery," Wright said.
Home gardeners can wait before removing the plant if they suspect Roundup residue, but that could allow rose rosette to spread to another plant, he said.
Rosa multiflora appears to be the rose most susceptible to rosette. No cultivars have been shown to be resistant.
Early detection is critical for control. Infected roses should be removed and destroyed. Roots left in the soil may re-sprout still having the virus.
Effective control of the mites can reduce the risk of rose rosette spreading. The pesticides Sevin and Avid are registered for control of the mite. Use of Sevin, however, may lead to outbreaks of spider mites.
More information about rose diseases is available online in the MU Extension guide "Roses: Care After Planting" (G6601) at http://extension.missouri.edu/xplor/agguides/hort/g06601.htm.
The MU Plant Diagnostic Clinic can assist gardeners with disease identification and plant diagnosis. For more information, visit the clinic’s Web site at http://soilplantlab.missouri.edu/plant/ or call 573-882-3019.