Elms on the rebound / Resistant varieties finally get chance to give shade
More than 70 years after Dutch elm disease began to wipe out 90 percent of the magnificent American elms that lined the streets of so many cities and towns, a handful of resistant varieties are beginning to cast their regal shade over the country's lawns and boulevards.
The fungus that causes the disease -- Ophiostoma ulmi -- accidentally entered the United States in 1931 on elm logs shipped from France and headed for Cleveland.
"It first showed up in Ohio and then New Jersey," said Alden Townsend, a plant geneticist at the National Arboretum for the U.S. Department of Agriculture, who has worked for 30 years to identify and propagate disease- resistant elms. "The fungus is carried from tree to tree by a bark beetle, and soon spread across the country."
By the 1980s, the fungus had wiped out 77 million American elms.
Now, two native elms are emerging not only as highly resistant (no elm is immune) to the disease, but with the same elegant vase shape and upheld branches that imprinted themselves on the American heart.
The 'Princeton' elm -- first propagated and planted in 1922 by Princeton Nurseries, now in Allentown, N.J. -- may be the prettiest. Several hundred were planted in the early 1930s, to form an allee on Washington Road, leading into the Princeton University campus. And 70 years later, the 60-foot-high trees form the kind of leafy canopy so many Americans had thought lost to history.
In terms of resistance to Dutch elm disease, the elegant, vase-shaped 'Princeton' is running neck and neck with 'Valley Forge,' a variety selected by Townsend from thousands of elms.
After the disease struck, Department of Agriculture scientists combed the country for resistant elms, propagating the most promising and inoculating them with huge doses of Dutch elm disease.
In Townsend's latest test, each tree base was inoculated with 3 million spores of the fungus. (A beetle would transmit up to 100 spores.) " 'Valley Forge' and 'Princeton' showed 96 percent resistance and 'New Harmony' was 86 percent," he said.
Both 'Valley Forge' and 'New Harmony,' Townsend's top selections and planted more than 20 years ago, "are looking good," he said. "They may survive 100 years, but we just don't know how they will do long-term."
However, a resistant elm is not necessarily a beautiful elm.
'Valley Forge' "may not be as nice a looking tree as 'Princeton,' " said Keith Warren, the director of product development for J. Frank Schmidt & Son, a 3,000-acre wholesale nursery near Portland, Ore., that ships 2 million trees a year.
'New Harmony' is not getting high marks for beauty either.
"It tends to be much twiggier," said Davis Sydnor, a professor of urban forestry at Ohio State University, who is working to bring elms back to Ohio.
Still, growers concede, these young trees, like ugly ducklings, may mature into beautiful swans. "The elms are coming very strong," Warren said. Shunned for 75 years because of Dutch elm disease, they are "now coming back as a different group of plants because of research and breeding work."
The Schmidt catalog lists 10 elm varieties, though 19 are growing in the nursery. " 'Valley Forge' is going to be very hard to find," Warren said. "The 'Princeton' is probably the best American elm in the most supply."
Such promising news gladdens the hearts of urban foresters who have long argued that the elm is about the best street tree there is, despite its susceptibility to disease.
When Cleveland was replanting its Public Square in 1978, Sydnor said, "They put a whole bunch of London plane trees in there. They all croaked."
The city then tried green ash honey locusts twice and oaks, but Sydnor said,
"So here they went through four separate replacements, when I knew the American elm would probably give them at least 15 to 20 years of service as a street tree.".
Elm trees are tough, Townsend agreed. "Even if you planted one without disease tolerance, it would tolerate ice and salt, air pollution, drought, some degree of flooding," he said. That's why the colonists loved them. "People would pull them out of the woods and they would just take off."
During the Industrial Revolution, cities found that the elm was one of the few trees that could tolerate "all that particulate matter from burning coal," Sydnor said. "But unfortunately, they planted it to the extreme, which led to a monoculture. Then came Dutch elm disease and the rest is history."
About four years ago, the Central Park Conservancy in New York planted a number of 'Princeton' elms at 104th Street and Fifth Avenue, as well as the park's Literary Walk, and they are doing fine so far.
In 1996, under Sydnor's prodding, Cincinnati planted 70 'Princeton' elms on Martin Luther King Jr. Drive, a highly compacted and alkaline site. They are now 30 feet tall, with trunks 8 inches in diameter. About 300 'Princeton' elms,
in fact, have been planted under the Cincinnati elm program, with an additional 100 due for planting this year.
Elm lovers may also choose from any number of highly resistant Asian and European hybrids like 'Frontier,' a 40-feet-high tree with exfoliating bark and wine-colored leaves in fall; 'Accolade,' a 70-foot vase-shaped tree with dark green glossy leaves; and 'Allee,' an upright Chinese variety that exfoliates with patches of cream gray, orange and brown.
WHERE TO FIND IT
-- Riveredge Farms, Atlanta; www.americanelm.com; (888) 680-1922. Carries the 'Princeton' elm.
-- Botany Shop, Joplin, Mo.; www.botanyshop.com; (888) 855-3300. Carries the 'Valley Forge' elm.
Locally, these elms and other promising varieties are often available only to landscape contractors or municipalities with access to wholesale nurseries. Your local agriculture extension agent or a reputable arborist is a good place to start.