Survey teams using hand-held computers are conducting a three-week inspection of more than 8,500 American elm trees along District streets, looking for wilting leaves, dead branches and other symptoms of the Dutch elm disease that has ravaged the species in recent decades.
The survey began last week and will end July 2. It will help pinpoint the extent of the disease in the elm population and guide efforts to keep it under control, according to the survey's sponsors, the city's Urban Forestry Administration, the National Park Service, the U.S. Forest Service and Casey Trees, a nonprofit group.
Four three-person teams are working Wednesdays through Sundays surveying the elms along city streets. They send their data once a week to the Forestry Administration, which is part of the D.C. Department of Transportation. City forestry officials will determine whether the trees are diseased. Mild cases will be treated with pruning and fungicide. Severely infected trees will be removed.
In the first five days of the survey, the teams looked at 2,451 elm trees and identified 91 with possible disease symptoms, Dan Smith, a spokesman for Casey Trees, said yesterday. The work is the first comprehensive disease check of elms along city streets in several years, he said. In the future, it may be expanded to include thousands more elm trees on other city properties, such as parks, and on private land.
"In the last few years, there has not been as aggressive of an effort for monitoring Dutch elm disease in the District," Smith said. "So we are all trying to work together to jump-start that."
Dutch elm disease is caused by a fungus and is spread by the elm bark beetle. It blocks a tree's water-conducting system and eventually kills it. Since it was detected in the 1930s, reportedly after being brought to the United States in a shipment of logs, the infection has killed as many as 100 million American elm trees, a widely planted species known for its graceful canopy.
In 1959, according to a recent report by Casey Trees, there were 38,250 American elm trees in the District, including those on federal land. There was an upsurge of the disease in the 1970s, and by 1993, a Park Service estimate put the number at 25,000.
The Park Service, which has 2,700 American elm trees along the Mall and on other land, has been more vigilant than the city in maintaining its stock. As they have each year about this time, park scientists are surveying their trees for symptoms of the disease, which typically show up in early summer.
Through monitoring and treatment, the Park Service has controlled the rate of disease, which affects 2 to 3 percent of its trees, said James Sherald, chief of natural resources and science for the Park Service's regional office.
"We still have a major commitment to the elm and do the best we can to protect the trees we have," he said. The tree, he said, is "a national icon."
Both the Park Service, on its land, and Casey Trees, on city streets, are planting recently developed disease-tolerant varieties of American elm. Since 2003, more than 600 Princeton American elms have been installed throughout the city, including 88 put in this spring along Pennsylvania Avenue in front of the White House.
The teams surveying city streets include summer interns hired by the city and volunteers who had Park Service training. They are checking 8,588 American elm trees identified in a 2002 street-tree inventory. They also are looking at 2,700 other trees identified as other varieties of elms to make sure they were named correctly.