Possibly the deadliest disease ever for roses in the U.S.

Button's front yard, surrounded by beds that were once all filled with roses. TOM GRALISH / Staff Photographer
Button's front yard, surrounded by beds that were once all filled with roses. TOM GRALISH / Staff Photographer
Posted: July 23, 2013

For a rose-lover like Catherine Button, it doesn't get much worse than this:

Over the last two years, she has lost 65 of 75 roses in her Burlington County garden to a strange-sounding disease known as rose rosette.

Though most home gardeners in the Philadelphia area have never heard of it, the disease may turn out to be the deadliest threat to roses ever.

Spread by a mite invisible to the naked eye, rosette affects many garden roses, including the heretofore bulletproof Knock Outs. It is impossible to prevent, difficult to contain, and has no cure. Infected plants must be destroyed - and they have been, in public and private gardens around the region and country.

It is the latest scourge to afflict the American landscape in the last decade, following sudden oak death, emerald ash borer, boxwood blight, and, most recently, downy mildew, which devastated the 2013 crop of impatiens, the best-selling summer annual.

"It's a jungle out there, it really is," said Bill Craig, nursery manager at Primex Garden Center in Glenside, who has destroyed 10 rosette-infected roses so far this summer and, like other growers and vendors, is closely monitoring his inventory.

Symptoms should be on full display right now: grotesque raspberry-red or unusual green growth toward the top of the plant; weak, pliable canes with an abundance of thorns, called prickles in the trade; misshapen buds that never open; and shriveled leaves.

The effect is sometimes mistaken for herbicide damage, but once fully infected, roses - since 1986, the nation's official flower - will die in two to five years.

"It's so sad. I really, really miss my roses," said Button, of Westampton Township, a rose-show competitor who has turned her attention to irises until a cure - or a rose with rosette resistance and all other qualities consumers demand - is found. It could be years.

The disease was first detected out West in the 1940s. From there, it spread slowly, unpredictably waxing and waning, arriving on the East Coast in the 1990s and in local gardens more recently.

The offending mites - eriophyids, North American natives - have four legs, a carrot shape, and cannot fly. They're carried randomly by the wind and are so small, it's said 20 could fit on the head of a pin.

Their primary host is multiflora rose, an Asian native brought to the United States in 1866 as root stock for grafted ornamental roses. For decades, starting in the 1930s, the U.S. Department of Agriculture, and agencies such as the Pennsylvania Game Commission, promoted multiflora rose as a "living fence" in fields and a crash barrier on highways. Its impenetrable thickets also provided food and cover for wildlife and worked well for erosion control and strip-mine reclamation.

Today, this wild rose with the pretty white and pink blossoms is considered an out-of-control, noxious weed, infesting an estimated 45 million acres in the Eastern United States alone. It rings a township-owned pond near Button's home.

Eventually, she knows, rose rosette disease will kill off those multiflora roses. Till then, they're a launching pad for mite attacks on the few remaining roses in her garden.

"The swatches of multiflora are much too large for one person to . . . start whacking," Button said. "We should get goats."

H. William Barnes, a rose breeder, wholesale plant buyer, and nurseryman for 40 years, first saw rosette disease around 2005. Lately, he has spotted infected Drift and Knock Out roses in front of Barnes & Noble in Willow Grove and St. Thomas Church in Whitemarsh - and in his own garden in Warrington, not far from a multiflora patch.

" Rosa multiflora is lurking around. Almost any property, anywhere, it's bound to be there," said Barnes, who has found three roses that may be vulnerable to other diseases but are less susceptible to rosette - Bonica, Chrysler Imperial, and Peace.

He is trying to breed a rosette-resistant rose.

Given the stakes, he has plenty of company, including Star Roses and Plants/Conard-Pyle of West Grove, Chester County, which has sold 80 million Knock Outs since 2000. Whoever creates a rose with the Knock Out's flower power, compact shape, and resistance to drought and disease - plus rosette protection - will surely hit the jackpot.

"It could be the next Knock Out, you might say," said breeder Michael S. Dobres, founder and managing director of NovaFlora, a Conard-Pyle subsidiary.

To solve the rosette conundrum, Dobres, smaller plant breeders, and hobbyists alike are looking to a handful of native American rose species - such as Rosa palustris or swamp rose - that are naturally resistant to rosette but lack the desirable qualities of modern hybrid roses.

Until that marriage is consummated, which could take a decade, experts urge gardeners not to panic. "This will be resolved down the line," said Terry Palise, president of the West Jersey Rose Society.

Do be vigilant:

Drastically prune roses in late winter or early spring to kill off nesting mites. Remove canes or stems at the first sign of the disease. Apply horticultural oils to prevent mites from getting a foothold.

If the whole plant gets infected, bag it up, dig out every bit of root, and throw it all in the trash.

"People love a rose, so early identification is key," said Dobres, who discovered rosette last year in a Drift rose in his city garden in East Falls.

As for alternatives to the much-loved rose, Button's got her irises. Others suggest rose of Sharon or butterfly bush.

But nothing else will do for Gus Banks, a retired Air Force navigator with 300 roses in his Eastampton, Burlington County, garden. "The only alternative to roses," he said, "is more roses."


Lucy Dinsmore, rose garden horticulturist at Morris Arboretum, looks for symptoms of rose rosette disease.


Contact Virginia A. Smith at 215-854-5720 or vsmith@phillynews.com.