Fresh on the heels of impatiens downy mildew and boxwood blight, a new malady may soon be blowing into Hudson Valley gardens: rose rosette disease. It’s a virus carried by tiny mites, and no effective controls are available for existing infected roses.
Rose rosette disease characteristics include excessive thorniness and witches’ broom growth, or clustering of small branches, as well as reddening, distorted, stunted and elongated leaves.
(Roses with symptoms typical of rose rosette disease seen in a recent planting in Queens. Photo courtesy Jason M. Compaan)
“I have seen it here in Rockland, but so far, it hasn’t been common,” says Amy Albam, senior horticulture/diagnostic lab educator with Cornell Cooperative Extension of Rockland.
“I’ve seen it on a couple of samples of garden roses,” she says. “One was a master gardener who brought it in and I’ve also seen it on samples of multiflora rose as well.”
“It looked like the stems were shortened and it had many, many more thorns than normal and it was somewhat distorted,” Albam says. “In the last three or four years, I’ve only seen three or four samples of it, so it’s not a huge problem at this point.”
Margery Daughtrey, a plant pathologist at Cornell’s Long Island Horticultural Research and Extension Center in Riverhead, says that the disease has so far been more of a problem in states south of New York. “It’s been in Virginia, Maryland, Delaware and south Jersey for a while,” she says. “The idea of it showing up in New York is new.”
“It hasn’t been a big panic for rose growers up to now,” she adds. It can be tricky to identify, looking like roses that have been hurt by an herbicide spray such as Roundup.
“Look for a lot of redness, on the stems and leaves, and a huge amount of thorniness,” Daughtrey says. “It’s very colorful looking — really bright red. And I’m talking super-duper thorny, compared to normal.”
“It’s a very conspicuous disease,” she adds. “It really can’t be compared to anything except that Roundup effect.”
“It’s something that has really gotten onto people’s minds in just the last few years, even though it’s been around for a long time,” she says. What’s changed is that “people are growing so many more roses in the landscape in big mass plantings.”
Traced to multiflora roses
The disease, first documented in 1941, is traced to the multiflora rose, which came from Japan in 1866 as a common rootstock for ornamental roses. Unfortunately, it was found that multiflora roses, which are known as wild roses, are bad because a single plant can produce a million or more viable seeds per plant; over time, these roses have become known as invasive weeds with enormous disease problems. Today, new roses like Knock Out and Drift are grown on their own rootstock.
Rose rosette disease has been spreading through much of the wild rose population in the midwestern, southern and eastern United States for years, according to research by Chuan Hong, a plant pathologist with Virginia Tech. Recently, it’s been confirmed in cultivated roses — Knock Out, Drift and Flower Carpet roses, to name a few popular types — in Virginia and other states.
“I received some rose rosette disease samples last year but nothing serious,” Hong says. “For sure, this disease is on the rise and we need to pay more attention to it.”
“Now that people are talking about it, I suspect we’ll see more and more cases,” Daughtrey says. “It’s very much news right now.”
“It’s too soon to know if it will be as much a problem in New York as it’s been in the South,” she says.
“By hearsay, I gather that there are nurseries in the South that are having a real problem with the disease.” Certainly that’s been the case for Anderson’s Home and Garden Showplace in southeastern Virginia. The nursery is selling no roses to customers and showcasing no roses in its display beds this season because of rose rosette disease.
“We have ripped out over 250 Knock Out roses in our parking lot to date that have been affected with the disease,” says Jason Blanchette, vice president. He says he knows of more nurseries nationwide that are abandoning roses.
The organic rose garden at the Virginia Zoo in Norfolk, Va., lost its entire 70-plant Knock Out hedge to the disease, as well as many Flower Carpet roses.
“It can blow in the wind or it can hitch a ride on other insects,” Daughtrey says. The good news is that “it does not spread quickly from plant to plant.”
She suggests starting by pruning out all affected parts of any diseased roses, but you may need to rip out and destroy the plant.
Star Roses and Plants by Conrad-Pyle, developers of Knock Out and Drift roses, are putting extensive research into the problem, says Steve Hutton, company president. They hope some of the native roses will provide answers. (A document about the issue is found on its website at www.conard-pyle.com/index.cfm/fuseaction/home.showpage/pageID/143/index.htm.)
“Some of the U.S. species with resistance to rose rosette disease are Rose palustris, R. arkansana, R. setigera and perhaps a couple others,” he says.
“The disease can infect any modern rose such as hybrid teas,” Hutton says. “Seems like anything with Asian roses in its background is susceptible — again, this is a theory, not yet proven.”
It’s not a soil-borne problem, but some suspect root-to-root contact can help spread the disease because so many shrub roses are being used in mass plantings. Good sanitation — picking up dropped rose petals and foliage — can help prevent it and other plant problems. Pruning is also crucial to keeping the problem away or under control — roses should be pruned in late winter or early spring, after new growth can be seen.
Prevention is key
Prevention is the best strategy, according to plant pathologist Hong. Buy healthy plant material, he advises, and fertilize and water plants as needed to keep their immunity strong.
“People including myself love roses, and roses will continue to be an important component in home yards,” Hong says. “A way forward is for rose societies, the public and science community to work together to find more effective control options for this growing disease problem.”
If you want to avoid the problem totally, there are many other flowering shrubs that will provide months of color in place of roses, including azaleas, butterfly bush, spirea, hydrangea and rose of Sharon.
Kathy Van Mullekom of the Daily Press in Newport News, Va., contributed information to this report.