Facing a spreading new blight in boxwoods

For more than 200 years, boxwoods have been a favorite in formal gardens and historic sites. At right, Colonial Williamsburg has a garden that includes many boxwood hedges.
For more than 200 years, boxwoods have been a favorite in formal gardens and historic sites. At right, Colonial Williamsburg has a garden that includes many boxwood hedges. (Colonial Williamsburg Foundation)
Posted: April 14, 2014

Deer and plants: As any suburbanite knows, it's a marriage made in horticultural hell.

But Chuck Feld thought he was in the clear. Although 30 deer regularly cruised through Birmingham Gardens, his four-acre wholesale nursery in West Chester, thousands of boxwoods he was cultivating remained blessedly untouched.

Feld's "box," as it's known, may have defeated the deer, but it was helpless against a new scourge: boxwood blight, which first showed up in Europe in the mid-1990s and in Connecticut and North Carolina in late 2011.

Since then, it has spread to 10 other states, including Pennsylvania, New Jersey, and Delaware, and three Canadian provinces. Exactly how it got here remains a mystery.

Boxwood blight is just the latest disease or pest to lay waste to some of our most popular plants in recent years, among them impatiens, roses, and ash, oak, and maple trees.

The bad actors can piggyback on plants shipped to the United States, where permits and inspections are required. But Joe Bischoff, a plant pathologist with AmericanHort, a horticulture industry association, says there's a greater threat: "It's likely that most of these pathogens come in . . . through the illegal and/or uninformed pathway through travelers' baggage."

Either way, boxwoods are difficult; they can show no signs of the problem within.

The blight cannot be entirely prevented or cured, and it ruined Feld's 2013. His boxwoods - 2,100, up to three feet tall, planted in the ground, and 2,300 small ones in pots - were either infected or would soon become so, and, as required by the Pennsylvania Department of Agriculture, had to be destroyed.

Over 20 days last fall, he incinerated the bigger plants with a propane torch and used a backhoe to bury the small ones in a 10-foot hole.

A $30,000 investment, gone.

Ironically, Feld, a veteran propagator and horticulture instructor at Williamson Free School of Mechanical Trades in Media, teaches a course in plant pests and disease. He was all too familiar with boxwood blight symptoms: stems with black streaks, leaves with brown spots, defoliation within a week.

"But I never expected it to strike so close to home," he says.

Though not native to North America, boxwoods have been a beloved stalwart in American landscapes for more than 200 years, especially in formal gardens and historic sites, such as Mount Vernon, George Washington's estate in Virginia; Colonial Williamsburg; the White House; and Arlington National Cemetery.

They are the third best-selling shrub in the U.S., a $103 million-a-year business. No wonder Bischoff calls the blight "a significant threat to the industry."

Lately, more consumers have come to appreciate boxwoods' deer resistance and drought tolerance, but its reputation was built on the fact that it's evergreen, adaptable to sun or shade, easily sheared into fashionable geometric shapes.

"And that lush green look is difficult to beat," says Dean Norton, horticulture director at Mount Vernon, which has had boxwoods since 1798 and today features more than 4,000.

Unfortunately, English and American boxwoods, the two most popular varieties, are also the most susceptible to Cylindroclaidium buxicola, the blight-causing fungus. Its sticky spores move from plant to plant in splashing water, on pruners, clothing, people, dogs and wildlife, and on defoliated leaves that blow around the landscape.

An English boxwood typically has more than a thousand leaves, each one capable of producing a couple of thousand fungal spores if infected.

The spores flourish more in shade than sun; tall boxwoods with good air circulation seem to do better than short, dense ones; and researchers have found fewer infections in hot, dry conditions than in warm, humid ones.

"When you introduce a new fungus, and you have two really, really, wet years [2012 and 2013], that got the fungus spread around the East Coast," says Kelly Ivors, a plant pathologist who studied boxwood blight extensively at North Carolina State University.

Complicating matters is the fact that some infected shrubs don't develop symptoms for a while. And that selectively removing sick plants doesn't eliminate the threat in a garden.

"It would just be a matter of time and distance for [the blight] to spread," says Ivors, who calls efforts to prevent or manage the disease "a work in progress."

Robert Saunders, sales manager for Saunders Brothers, his family's 99-year-old, wholesale nursery in Piney River, Va., says growers initially panicked over boxwood blight. Now, they're looking to propagate and promote newer varieties with some degree of tolerance.

"It's inevitable that we're going to see blight, but if we can focus on new varieties and educate people, we'll be able to face it better," says Saunders, who supplies boxwoods to Mount Vernon, the White House, Smithsonian Institution, and other landmarks.

Longwood Gardens in Kennett Square, too.

Boxwood has been a signature plant there since its days as a private estate. When it became a public garden in the early 20th century, a Sunken Boxwood Garden was installed where the Main Fountain Garden is today.

Today, more than 2,000 boxwood hedges, topiaries, and individual specimens, some more than a century old, dot Longwood's lawns, gardens, and allées. And Grant Jones, who oversees pest management, is employing a host of "best practices" for their care.

Tools are sterilized, irrigation systems closely regulated. Old boxwoods are monitored; new ones are quarantined for 90 days and sprayed with fungicide.

"So far, so good," Jones said. "We haven't seen any blight."

Feld worries about consumers and landscapers who don't know about the blight or follow "best practices." They might prune infected, asymptomatic boxwoods and fail to sterilize their tools. They might leave infected leaf litter on the ground, toss it on the compost pile, or put it on the curb to be collected for municipal compost or mulch.

Some advice:

If you have boxwood, be vigilant. If you want boxwood, choose a relatively blight-tolerant variety, like Green Beauty. And buy from a reputable nursery.

"Not one of those places by the side of the road," says Feld, who now cultivates plum yews instead of boxwoods. Deer don't like them either.


vsmith@phillynews.com

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