The Washington area is in the midst of an epidemic of Dutch elm disease that is escalating rapidly and could kill most of its American elms within the next few years, an expert from New York State said last week.
Several U.S. cities such as Hartford, Conn., and Cleveland already have lost virtually all their American elms, and other parts of the country have been losing elms at varying rates to Dutch elm disease (DED), a fungus discovered in the Netherlands and spread by elm bark beetles, which apparently came into this country in the 1930s on imported elm logs.
Gerald N. Lanier, who for the past three years has been experimenting with methods of fighting DED in elms in various cities around the country, last year extended his experiments to Chevy Chase and, this year, expanded operations to include much of Northwest Washington.
Washington has about 18,500 American elms among the 104,000 trees that line its streets, according to Hans Johannsen, chief of the city highway department's tree division.
Until 1973 no more then 1 percent of Washington-area elms died from DED each year, according to city officials, a rate of attrition that is considered normal for trees on city streets.
But recently, Washington has been losing about 3 percent of its elms each year, city officials say. Lanier insists this estimate is low. He said his own survey has found there are many more diseased and dying trees than appear on city lists.
Lanier said his survey shows local elms are now dying at a rate of 6 to 10 percent a year. "This probably will escalate further, like an epidemic," said Lanier. "It should increase explosively over the next few years," despite continued efforts to spray the trees with insecticides.
Lanier and colleagues at the Syracuse campus of New York State University's college of environmental science have been experimenting with the so-called "tree-trap" method of fighting DED. The project, sponsored by the Freshwater Biological Research Foundation, has been financed with an anonymous $5,000 gift from a Washington-area resident.
The Northwest Washington and Chevy Chase experiment came to public attention two weeks ago, when more than 100 elm trees in those areas died almost simultaneously.
Lanier and his colleagues killed the dying trees quickly by injecting them with poison and by cutting the bark around them. If a diseased tree is killed quickly rather than being allowed to die slowly of DED, the autumn larval cycle of the elm bark beetle -- which would mature the following spring -- is interrupted and about 95 percent of the eggs die, Lanier said. Killing infected trees quickly also can stop the spread of DED to nearby elms through the roots, since trees growing close together often graft roots.
As part of Lanier's "tree-trap" experiment, many trees also were doused with a chemically produced pheromone, a substance that attracts elm bark beetles to weakened trees to feed and breed, since trees under stress give out a different odor than healthy trees.
The addition of a chemical pheromone attracts beetles from up as far away as a quarter of a mile, Lanier said. Thus the beetle populations in badly infected trees are killed, and other beetles are attracted to a tree they can no longer feed or breed on sucessfully.
Lanier said his university is looking for another private donation to pay for expansion of the experiment into other sections of Washington next year.
"The city has told us it has no money to do anything, although they are spraying with methoxychlor (a pesticide substitute for DDT)," Lanier said.