Bruce Carley, in his article on saving American elm trees from Dutch elm disease, paints a pretty picture of Main Street USA in the first half of the 20th century. It was a street typically lined with these majestic giants, which unfurled their weeping branches Rapunzel-like over the heads of passersby, affording shade on hot summer afternoons. There was no other tree quite like them. But the nightmare of the disease brought about a swift demise to scenes such as the following:
"The interweaving limbs of the stately trees that lined the streets ascended into a towering canopy with a graceful, arching beauty...spreading horizontally at heights often greatly exceeding 100 feet...." [Bruce Carley]
Dutch elm disease (Ceratocystis ulmi) changed all that. Dutch elm disease is a wilt fungus that grows in the sapwood of elms. The fungus was first encountered in 1921 in the Netherlands. Over the next few years elms across central and southern Europe were found to be succumbing to the fungus.
History of Dutch Elm Disease: The Demise of American Elm Trees
But American elm trees (Ulmus americana) are the most susceptible of all to Dutch elm disease. American elm trees are also known as water elms, soft elms, white elms or Florida elms. American elm trees are found throughout Eastern and Central North America. Their range extends as far south as northern Texas and Florida.
Cleveland, Ohio witnessed the first case of Dutch elm disease in the U.S., in 1930. Apparently, this silent killer arrived in a shipment of logs from France. But Dutch elm disease spread East quickly: Within two years American elm trees in New Jersey were falling prey to the deadly fungus.
The Dutch elm disease had "killed 77 million trees by 1970," wrote Phil McCombs in a 2001 Washington Post story that begins with this picturesque description of how American elm trees once lined the streets of many a town:
"Once upon a time in America, great leafy high-arching cathedrals of elms lined the streets of villages and cities from the Atlantic to the Rockies, casting a deep cool shade upon life's turmoil."
Why Dutch Elm Disease Hit American Elm Trees So Hard
For all the tranquility such mass plantings bestowed, this monocultural practice was one of the culprits in the downfall of American elm trees. The deadly fungus, it turns out, can spread underground from the roots of one victim to the roots of another nearby. This is what happened when the roots of adjacent American elm trees "grafted" together, essentially linking the lives of what had been two distinct entities.
The demise of one thus became the demise of the other. The monoculture and its consequent root grafting meant that infected sap could pass from one American elm tree to another in a chain reaction that would decimate a whole row along a street. But the planting of American elm trees en masse was not the sole culprit. The microscopic spores of the fungus are also transmitted from diseased victims to healthy specimens by two kinds of beetle that tunnel under the bark. One is a European bark beetle (Scolytus multistriatus), an import that preceded Dutch elm disease itself. The other beetle is a native bark beetle, Hylurgopinus rufipes. Photos of both of these carriers of Dutch elm disease can be found at the Forestry Service Web site, as well as photos of specimens damaged by Dutch elm disease.
There are measures that you can take to lessen the likelihood of Dutch elm disease spreading to established American elm trees that you have on your landscape. We'll consider those options on Page 2. But are these measures merely delay tactics, postponing an inevitable extinction looming over the near future? Could American elm trees ever regain their place as the country's shade tree of choice? Or will Dutch elm disease eventually catch up to its last remaining representatives...?