Rose rosette: A deadly virus of roses

“Extension on the Go” podcast by Debbie Johnson. Episode 138

COLUMBIA, Mo. – Rose rosette is a fatal disease of roses. There are no resistant varieties and infected rose bushes must be destroyed, even the roots.

“It has been identified as a viral disease that’s specific to the genus Rosa, including Rosa x hybrida, which is our prized garden rose,” said David Trinklein, horticulture specialist for University of Missouri Extension.

Trinklein says the disease started in wild roses (Rosa multiflora), which are considered a noxious weed in many states. So there was delight that a natural biological control for wild roses was found. That is, until the virus infected garden roses too.

The culprit that’s transporting this rose plague is a tiny mite.

An eriophyoid mite spreads the virus, Trinklein said. For gardeners familiar with the two-spotted spider mite, the eriophyoid mite is only a quarter the size of a spider mite and nearly impossible to see with the naked eye. They can’t fly, but wind can carry these tiny, lightweight mites. If the mite has the virus in its gut and alights on a rose bush, one bite will infect the plant.

Once infected, you cannot prune the disease away.

“Viruses are systemic to the plant. It’s in all parts of the plant all the way down to root system,” Trinklein said. “There is no cure, and it’s a slow death for the rose bush.”

The symptoms are very distinct, Trinklein said. First, leaves will unfurl malformed. As the disease progresses, the plant will produce excessively thorny, rosy-purple stems with feathery leaves. The common term is “witches’-broom.” The plant will stop producing flowers and eventually die.

To keep the infection from spreading, gardeners need to tear out the plant, including the roots, he said. Carefully place all the plant material into a bag and take it somewhere where it can be destroyed. Be sure to wash your hands after handling diseased plant material.

Before destroying a rose bush, verify that it is actually infected with rose rosette. Take a picture and send it to your local MU Extension center or to a local Master Gardener, Trinklein suggests.

Because the disease is so devastating, plant scientists and horticulturists are searching for a way to protect roses from infection. No effective controls for the mites have been found, Trinklein said. Typical miticides that work well on the two-spotted spider mite have little effect on the eriophyoid mite. Some authorities have suggested using pesticides that act as suffocants, like horticulture oils or insecticidal soaps. But the chances of controlling the mite before it starts feeding are very remote, he said.

Mites aren’t the only way rose rosette can spread.

“It can be spread during the grafting process, which is a common production practice for most garden roses,” Trinklein said. “This makes it very important that you purchase roses from a reliable source.”

Time heals all and for rose rosette, it will take time to stem the tide.

“When the wild roses are eventually killed by the disease, then that host will no longer act as a reservoir for the virus,” he said. “Once we get rid of that natural storehouse of inoculum, then it will be more difficult for the disease to spread.”

In the meantime, don’t give up on roses, Trinklein said.

“Gardeners are an optimistic, hardy lot, and this too will pass.”

For more information on rose rosette, go to http://ipm.missouri.edu/meg/2011/7/Rose-Rosette-Disease.