A New Beetle Invasion Threatens To Take Down Area Ash Trees
My neighbor lives on a rolling hillside dominated by lawn and trees. He has taken out a lot of the scrub over the years to show off trees of various species and age, and the place has the feel of an arboretum about it. His prettiest tree is a white ash, perhaps a century old, that has become stout in its sunny and open site. The ash is about 70 feet tall, with a spread of 40 feet or more and a round-topped crown.
Ash trees are not consistently fabulous for fall color, but here, too, my neighbor has hit the jackpot: His turns a uniform rich golden yellow, and at its peak it illuminates the world around it. When I saw it last October, the experience was tinged with sadness, knowing that this spectacle may be denied future generations.
The white ash and its close cousin, the green ash, are in a life-and-death struggle with an insect pest new to these shores. A small, metallic-green beetle named the emerald ash borer was discovered in Michigan in 2002, probably carried from its native Asia in packing cases. Since then, the beetle has caused the demise of 30 million ash trees in Michigan alone. The beetle lays eggs on the trunk, and the hatchlings burrow into the tree and create tunnels that disrupt the flow of water and sap. Infested trees show dieback in the canopy and, often, sprouts growing from the lower trunk. While Maryland authorities have been fighting to contain an isolated pocket of infestation in Prince George's County, the borer has spread to parts of Wisconsin, Illinois, Indiana, Ohio, Pennsylvania and West Virginia. The pest was found in Northern Virginia in 2003 but eradicated. Or so we thought.
New outbreaks in Herndon and Newington, near the Springfield Mixing Bowl, were confirmed last month and have brought a gloomy new complexion to the threat. For some, the notion has shifted from one of containing the pest to accepting that it is now among us. "It's here," said Jeremy Hager, an arborist with Bartlett Tree Experts who discovered the Newington infestation in 27 trees in a townhouse community. About 30 were affected in Herndon.
In July, the Virginia Department of Agriculture and Consumer Services established a quarantine area that consists of Fairfax, Arlington, Prince William, Fauquier and Loudoun counties and the cities of Alexandria, Fairfax, Manassas and Manassas Park. Ash trees and hardwood firewood can be moved freely within the area but not outside it. The department is not proposing the removal of trees on private and public property in zones around the outbreak, as Maryland authorities did in Prince George's.
For homeowners like Patricia and Edward Garner in Chevy Chase and my neighbor in Alexandria, the issue is what can be done to save beautiful old trees. The Garners' white ash is about 60 feet high and is one of a number that were either planted or self-sown when their neighborhood was built in the 1930s. "If I could do something preventatively that would not harm the tree, I would probably do it, unless it's prohibitively expensive," Patricia Garner said.
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Arborists and other landscape professionals have access to chemicals and formulations not available to consumers. Hager questioned the effectiveness of homeowner-applied drenches and said scientists in his company recommend a soil injection of concentrated, professional formulations of imidacloprid in a product called Merit as well as two foliar sprays using another class of pesticide called pyrethroids. Such treatments might cost $400 annually, he said, though fees vary by such factors as tree size and site access. One client, he said, has an ash tree that is 100 feet tall and 70 inches in trunk diameter. "It's going to cost over $1,000 just for the Merit application," he said.
His company has been treating the ash trees at Mount Vernon since the pest was discovered in neighboring Prince George's County.
George Washington's estate has a dozen old ash trees in and around the Bowling Green, the two oldest dating to 1819, 20 years after Washington died, said Dean Norton, Mount Vernon's director of horticulture. "They're not living witnesses [to Washington], but certainly they are historic trees," he said.
His aim is to remove two ailing ashes (one is leaning badly; the other has an incurable disease called ash yellows) and then remove the younger ash trees that grow in the estate's outlying woodlands. Those are mainly green ash, as opposed to the more stately white ash near the mansion. Norton worries they will draw the borer to his specimen trees.
"I only have so much money. Every ash tree around the mansion I'm going to protect," he said. "I just can't protect everything."
Perhaps in a few years, visitors will go to Mount Vernon just to see what ash trees look like. The green ash in particular has been a common street tree, but its days appear numbered.
Paige Thacker, horticultural extension agent for Prince William County, said she is not advising residents to apply preventative treatments. "It's introducing a pesticide without knowing for sure [the pest] is there," she said. "If you're in Newington, then maybe, or Herndon."
In Chevy Chase, the town's arborist, Tolbert Feather, said he has no plans to treat street trees preventatively. "It's just too much expense and maintenance," he said, "and I don't like using [imidacloprid] on that wide a scale."
The pesticide is highly toxic to bees, and scientists are studying its role in the widespread death of honeybees, a condition known as colony collapse disorder. It almost goes without saying, of course, that this whole mess rests with one species of animal, Homo sapiens.