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They’re back! American elms are on the rebound

After several decades, when many horticulturists believed it was heading for extinction, the American elm is making a comeback.

Along with other icons such as the Bald Eagle and the Grand Canyon, the majestic American elm seemed to stand as a homegrown hero, representing this great nation. But then the unthinkable happened.

In 1930, a stowaway beetle clinging to a log arrived in Cleveland on a ship from England. (Or it was on a ship from France in 1931. Both versions of the story have circulated for years. Take your pick!) The little bug brought Dutch elm disease to America. It’s a disease that has killed hundreds of millions of trees worldwide and wiped out at least 95% of our lofty American elms as they had no resistance to this foreign invader.

Rapidly, tree-lined boulevards and avenues in almost every American city and suburb were stripped of their shade and elegance as elm after elm succumbed to the disease. Total extinction, the end of the species, seemed a real possibility.

But the search began for ways to develop disease-resistant elms, and evidence suggests that, at long last, a healthy American elm is a reality. Nowhere is this more evident than on the streets of Washington, DC.

The Casey Tree Endowment Fund (CTEF) is dedicated to “re-greening” the nation’s capital and set itself an objective to fill 23,000 empty tree spaces within ten years. The folks at Casey are centering their efforts on a species known as the ‘Princeton’ American elm, because of its apparent resistance to the dreaded Dutch elm disease.

The Princeton is named in honor of a giant elm tree that stands in a cemetery on the corner of Witherspoon and Wiggins streets in Princeton, NJ. It has grown there for more than 300 years, and photos from 1854 show it, tall and healthy, near to Aaron Burr’s grave. This massive tree is believed to be the progenitor of a whole generation of disease-tolerant elms that are now finding their way around the country.

Thanks to that old tree in Princeton, and to the dedication of people such as those at CTEF, disease-resistant elms have taken root on the pedestrian mall along Pennsylvania Avenue in Washington, DC, as well as on the grounds of the White House itself.

However, Dutch elm disease is by no means eradicated and is still a threat. If you are fortunate enough to have a healthy elm tree as part of your landscape, you need to keep watch for signs of the disease. It is caused by a fungus that grows in the tree’s xylem tissue and attacks its “plumbing system,” causing yellowing and discoloration of leaves, twig and branch dieback, premature defoliation, and often the death of the tree.

What are the signs that should alert you to a potential problem?

In addition to the discolored leaves, look for brown streaks if you cut into the sapwood of infected branches. The disease may progress slowly or kill the tree within a week after you notice symptoms, according to http://forests.org/articles/reader.asp?linkid=31481 a Web site hosted by the Forest Conservation Portal. You can click on a direct link when you visit my Web site www.landsteward.org and find this column under “The Plant Man” heading.

According to the Forest Conservation people, the only positive way to determine if your tree has the disease is to isolate and culture the fungus. Send samples from suspected trees to a diagnostic laboratory. Select twigs about 6 inches long that show brown streaking of the wood just below the bark.

Dutch elm disease spreads rapidly from tree to tree via intertwined roots below ground. Roots are more likely to intertwine when elms are growing less that 40 feet apart. I recommend a visit to this site if you have any worries about Dutch elm disease or its detection. As always, I’m happy to answer personally any questions or comments you send me via e-mail.

Yes, we still need to be aware of the dangers of this deadly disease. But the good news is indeed VERY good. Disease-resistant American elms are making a comeback. I’m looking forward to a stroll along Pennsylvania Avenue someday, looking up at the sun-dappled canopy of healthy American elms!

The Plant Man is here to help. Send your questions about trees, shrubs and landscaping to steve@landsteward.org and for resources and additional information, or to subscribe to Steve’s free e-mailed newsletter, visit www.landsteward.org