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Rose disease poses threat to local gardens

Tuesday, May 28, 2013
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These roses, which bloomed last July at a home in Saratoga Springs, are healthy. But some roses around the Capital Region have developed rose rosette disease, which is caused by a tiny mite.
These roses, which bloomed last July at a home in Saratoga Springs, are healthy. But some roses around the Capital Region have developed rose rosette disease, which is caused by a tiny mite.

— Dave Gade heard talk of rose rosette disease for 20 years before he ever saw any sign of it.

As garden operations supervisor for Schenectady’s Central Park Rose Garden and a master rosarian with The American Rose Society, he has tended a lot of roses during the 40-plus years he’s been coaxing the thorny perennials to grow.

But it wasn’t until recently that the disease, which has been on the radar in the U.S. since the 1940s, hit close to home.

Two years ago, Gade received phone calls from two Capital Region residents whose rose bushes had mysterious ailments. He went to take a look, and diagnosed both cases as rose rosette disease.

“I was very surprised because I had never seen it,” he said.

Rose bushes affected by the disease can exhibit a variety of symptoms, including bright red leaves, excessive thorns and the growth of bushy clusters of short branches known as “witches’ brooms.” Rapid elongation of new shoots can also occur, along with flower distortion and stunted leaves.

Rose rosette disease is vectored by a tiny mite that can be transported long distances by the wind. The disease can also be spread by grafting.

Its symptoms were first reported in the U.S. more than 70 years ago, but the likely cause — the Rose rosette virus — was unknown until 2011.

Last summer, the disease reared its head in Gade’s home garden, in a bush that had been in his yard for 25 years. He also discovered it in several of the 4,000-plus bushes in the Central Park Rose Garden.

His rose garden volunteers are now on high alert, all trained to recognize the disease’s symptoms, which he said become evident around July, when the bushes have plenty of leaves and are in bloom.

No known cure

There is no known way to cure the virus, so infected plants must be dug up and disposed of.

“It’s kind of disappointing when you’ve got to throw a nice bush that looks healthy away, but by leaving it in you’re encouraging it more to spread,” Gade said. “You get rid of it, you’re getting rid of the problem.”

The invasive wild rose Rosa multiflora is highly susceptible to the disease, and it can spread from there to cultivated rose varieties. That’s what Gade thinks happened in his yard.

“Years ago, I had a multiflora rose come up and it was pretty. I just left it there, but with all this situation with finding a [diseased] bush in my garden, I took the multiflora out, too,” he said.

George Robinson, a biology professor at the University at Albany, said removing multiflora rose plants from the vicinity of cultivated roses is a good idea.

Insecticides can be used on cultivated rose bushes to battle the mites that transmit the disease, but they can sometimes cause just as much damage as the virus, Robinson noted.

“You’re also killing off a lot of the predators that eat the mites,” he explained.

There’s been no sign of rose rosette disease in Jackson’s Garden on the Union College Campus in Schenectady, and in Saratoga Springs, Yaddo Gardens’ 250-plus rose bushes are all still disease-free as well.

Although rose rosette disease hasn’t hit Yaddo’s rose bushes yet, those who tend them are watching for it, said Ralph Vincent, a member of the Yaddo Garden Association and a consulting rosarian with the American Rose Society.

Vincent is also on the lookout for signs of the disease in his home garden, where more than 100 rose bushes grow.

“I’m keeping an eye out for it right now, so that if it does occur, I don’t have to take any more shrubs out of my garden than I have to,” he said.

Suggestions

To help prevent the mites from infesting roses, Vincent recommended keeping shrubs healthy, well fed and watered, and free of dead foliage and branches. He also suggested keeping garden beds free of debris, and diligently checking bushes for the disease’s symptoms.

If a rose bush is suspected of harboring the disease, it’s important to dig out all of its root material, Robinson said.

Gade also recommended sterilizing the tools used for the job, to help prevent spreading the disease.

To date, no cultivar has proven resistant to the disease, but that shouldn’t make gardeners wary of growing roses, Vincent insisted.

“There’s problems with probably most garden plants out there that could happen, but I don’t think people should be afraid of growing them by any means,” he said.

 
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