RALEIGH — City parks officials are digging up infected rosebushes in hopes of stopping the spread of a disease that has struck plants in a Hillsborough Street roundabout and the renowned Raleigh Municipal Rose Garden.

Only four bushes in the 6.5-acre rose garden have been diagnosed so far with rose rosette disease. But they include large, climbing bushes on three prominent arbors at the garden off Pogue Street in West Raleigh, behind the Raleigh Little Theatre.

Garden workers recognized distinctive symptoms of rose rosette, including “witches’-broom” clusters of small branches. The diagnosis was confirmed by the city’s private contractor, Witherspoon Rose Culture. Other symptoms can include stunted leaves and a profusion of thorns.

“The witches’-broom is a deformation of the new growth as it comes out,” said Wayne Schindler of the city parks and recreation department. “It looks very abnormal. The disease can persist in a plant for six to eight years before the plant dies. The problem is if you leave the plant in place, it will affect all the other plants.”

City workers will bring in large equipment Tuesday morning to dig out the four diseased bushes, Schindler said. A 25-year parks and recreation veteran, Schindler said he cannot recall another time when the city found it necessary to remove diseased bushes from its popular rose garden.

On Friday, parks workers cleared out all the rosebushes in the center of the roundabout at the N.C. State University Bell Tower. They’ll be replaced with lavender and other perennials, Schindler said.

Botanists think that rose rosette disease came to the United States in the 1930s with the wild multiflora rose, a Japanese import that since has spread widely across the nation. It is caused by a virus and spread by a tiny, wingless mite that moves with the wind. There is no chemical treatment for it.

“This disease has been around for a while, and it seems to have become an increasing problem over the last several years,” said Mike Munster, an N.C. State University pathologist who diagnoses plant diseases for nurseries and commercial greenhouses.

Munster spotted a few infected bushes on the NCSU campus last weekend, and he recommended that the university landscaping department remove the bushes.

“It was the first time I had seen it on campus,” Munster said. “It’s a systemic disease, being a virus. So the plant is likely to have it even if you try to prune out the infected parts where you see the symptoms.”

Raleigh’s rose garden is a popular spot for weddings and other special events.

Schindler said garden workers and volunteers will watch closely to see whether the symptoms spread. He hopes eventually to plant new climbing roses for the picturesque arbors.

“This is something that’s very unique, that there is no cure for,” Schindler said. “So we’ve got to take some pretty significant action to prevent it from spreading.”

Siceloff: 919-829-4527 or blogs.newsobserver.com/crosstown or twitter.com/Road_Worrier/