The blight also poses a threat to the boxwood shrubs in our own gardens. The disease was recently detected in Northern Virginia for the first time — in a retail nursery and in a garden in Fairfax County. Infected plants show leaf spots that spread to destroy foliage. The stems develop black lesions. Untreated plants die.
Once the disease appears in old, established and treasured stands of boxwood, the plants can be kept alive only by a regimen of care that includes preventative spraying — burdensome and costly for places like Colonial Williamsburg and other historic sites.
If boxwood blight took hold in the Colonial capital of Virginia — now a major tourist attraction — “I would have better days,” Viancour said.
Although the disease spores don’t travel far on their own, they can be spread by introducing and handling infected plants. The nursery trade is working to keep infected plants out of the supply chain. The Northern Virginia nursery, which wasn’t named, has destroyed its inventory of boxwood, said Adria Bordas, horticultural extension agent for Fairfax County.
The spores can also spread, though, in boxwood harvested as holiday greenery.
Colonial Williamsburg uses boxwood along with other traditional material for the wreaths, ropes and swags that spruce up doorways and interiors of historic houses, but it also sells ready-made wreaths to visitors.
The boxwood comes from Colonial Williamsburg and offsite locations where boxwood is either harvested or made into wreaths. In each case, Viancour said, the boxwood is inspected by an expert for signs of the disease beforehand.
At Mount Vernon, “anything we cut is from the estate” to avoid bringing in the disease, said Dean Norton, director of horticulture. And shrubs that are brought in for planting come from a major Virginia boxwood grower who has “been on top of this from the beginning,” he said.
How can the consumer prevent spreading this blight with holiday greenery? In Virginia, in theory at least, shoppers can ask sellers whether their boxwood came from a supplier who has signed the state’s Boxwood Blight Cleanliness Agreement, which maps out practices and state inspections.
These tips from Virginia Cooperative Extension might be of more practical value:
●When you buy greenery, look first to see whether it might be blighted with leaf spot, browning, black streaks on stems and leaf drop. You can see pictures at www.bit.ly/1iHNtNx.
●Assemble wreaths away from any existing boxwood plantings. Sterilize garden tools after use with alcohol or a chlorine solution.
●After the holidays, put wreaths and fallen debris in trash bags, preferably double-bagged for the trash and landfill. Don’t try to recycle wreaths in the landscape, including compost piles.
“There’s going to be a certain risk with greenery,” said Larry Nichols of the Virginia Department of Agriculture and Consumer Services. “A homeowner, at the end of the season, should make sure they dispose of it properly.”
As for actual plantings, the two most traditional boxwood varieties — the slow-growing and billowy English box and the tall, upright American box — seem to be highly prone to blight.
If I had irreplaceable old specimens in my garden, I’d probably not bring in any new boxwood plants for a while. It’s worth noting that if you see browning of your boxwood branches, it is not necessarily the blight disease. English box is notoriously sickly, and it discolors for a number of reasons, including placement in wet heavy soil and exposure to winter sun and winds. You can take a specimen to your local extension agency for testing.
I like some of the newer hybrids, which give the fine textured boxwood effect without having to wait a lifetime for measurable growth. Several of them, it turns out, are tolerant of the blight.
Plant pathologists at North Carolina State University tested varieties against the blight and found Green Beauty, Nana, Harland box and Golden Dream to be tolerant; Winter Gem, Dee Runk, Fastigiata, Green Gem and John Baldwin were moderately tolerant. The most susceptible were English box and, sadly, a handsome and otherwise tough variety named Justin Brouwers.
Green Beauty, Green Gem and Nana all do a good impersonation of English box. Because these resist the blight, they can spread it to weaker varieties. Again, be careful if you have existing mature plantings.
Although Williamsburg has fended off the blight, the gardeners have changed some practices to reduce its chances of getting a foothold.
Shearing hedges of English box gives a dramatic edge to them but causes congested growth at the branch tips, which, in turn, harbors any sort of fungal disease. It is better to thin out the shrub by removing selected branches; this “plucking” creates barely perceptible gaps that encourage future full and healthy growth.
Another sound practice is to water the plants at the soil line, not with overhead irrigation.
While we tiptoe around this disease, plant hybridizers are working on developing more varieties that can deal with it.