Dutch Elm Disease Takes Toll on Urban Canopy
April 29, 2015
PROVIDENCE — Elmhurst, Elmwood, Elmgrove. In a city with neighborhoods, streets and diners named after the stately elm, the iconic tree is increasingly in peril. In late March, another century-old American elm was felled on the property of the John Brown House on the city’s East Side. Over the past two and a half years, elms on the property have been succumbing to disease.
The tree felled on March 31 tested positive for Dutch elm disease, according to Tom Morra of T.F. Morra Tree Care, which has been hired by the Rhode Island Historical Society to remove dead elms from the property and preventatively treat the remaining healthy trees.
Dutch elm disease is one of the most destructive shade tree diseases in North America, according to the U.S. Forest Service. The disease kills individual branches and, within one to several years, the entire tree. It’s mainly transmitted between trees through grafted root systems or by the elm bark beetle, according to Morra.
Additional elms at the north end of the property already display symptoms of Dutch elm disease and are beyond the point where treatment can save them, Morra said. Elms on the south end of the property currently appear unaffected, he said.
Morra said there are three different products the Historical Society can choose from to prevent the disease from spreading to the remaining elms, though he noted that no treatment guarantees the trees will remain healthy. Depending on the product, treatment must be repeated every one to three years. Each product requires drilling holes into the trees’ trunks for injections.
Arbotect, the product that offers the longest period of protection (three years), is the only available one that has been shown to both prevent Dutch elm disease and cure trees exhibiting early signs of the disease, according to Morra.
Regardless of the product chosen, the threat of Dutch elm disease will not dissipate and the trees will become more susceptible as they age, he said.
All but one of the centenarian trees on the John Brown House property, at the corner of Benefit and Power streets, are American elms, which are very susceptible to Dutch elm disease. One English elm also grows on the property and, according to Morra, is more resistant to the disease.
In place of the felled elms, the Historical Society has planted Princeton elms, which, until recently, were thought to be resistant to Dutch elm disease. Now, even this variety has proven susceptible to the disease. Morra said he will not plant any more Princeton elms on the property in light of the new information.
Morra said the decision about which species of trees will replace the elms on the property is up to the Historical Society. He said he will suggest the pin oak as a stately, disease and decay resistant option. C. Morgan Grefe, the society’s executive director, said the organization will likely avoid replacing the elms with another monoculture.
“This has been rough on all of us,” Grefe said. “The elms are a defining feature of the John Brown property. It’s heartbreaking.”
Recently, Grefe found a document in the archive with instructions for protecting the elms on the John Brown House property from Dutch elm disease. The document is dated 1957 and makes note of the property’s 20 elms. Today, about half remain.
“This is a conversation we have been having about these trees for more than half a century,” Grefe said.
Dutch elm disease has been ravaging urban elm populations since the disease was introduced into America from Europe in the 1930s.