Extension News

New Elms on Trial

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Yard and Garden Column for the Week Beginning May 6, 2005

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By Mark Gleason
Plant Pathologist
Iowa State University Extension

When we last left the American elm it was not just down, it was out. From the 1920s through the 1980s, Dutch elm disease swept through the northern U.S. like a Biblical pestilence, leaving millions of dead trees in thousands of towns. Today, only middle-aged and elderly people remember the soaring grace of elm-lined boulevards.

Nobody was more traumatized by this debacle than plant pathologists. The public looked to plant disease specialists for help against Dutch elm disease, but our best efforts barely even slowed the epidemic.

So maybe it’s not surprising that plant pathologists are leading an elm revival. For decades, plant breeders have been quietly seeking elms that can fight off Dutch elm disease. Today, we finally have some elms that could re-take the urban landscape. 

The new elms are a diverse bunch.  Some, like the cultivars ‘Independence,’ ‘New Harmony,’ and ‘Valley Forge,’ are true American elms, with naturally high levels of resistance to Dutch elm disease. Others are Asian imports with built-in resistance, since they evolved with the fungus over many millennia. Still others are hybrids of Asian and American elms. 

The elm comeback has been a slow and cautious one. For one thing, people who harbor painful memories of the Dutch elm disease epidemic may see elms as too risky.  You can find some of the disease-resistant elms in larger garden centers, in catalogs, and online, but you have to look pretty hard.

Another reason for the slow revival of elms is that we are still learning the pluses and minuses of the new selections. Generally, elms are wonderfully well adapted to common rigors of urban environments like drought, compacted soil, and limited rooting area. But we need to know more about their regional adaptability. Can they tolerate the climate and other challenges of life in Iowa?

The need to know more about the new elms was the driving force behind the National Elm Trial. At 19 locations throughout the U.S., 14 elm cultivars, all resistant to Dutch elm disease, are being planted in spring 2005. The trees will be scrutinized over the next 15 or so years.  Notes will be taken on their hardiness and tolerance to such pests as the elm leaf beetle and elm yellows disease.  Results from the National Elm Trial sites will gradually reveal which elms thrive best in each part of the country.

In Iowa, the National Elm Trial trees are being planted at the Iowa State University Horticulture Research Farm near Gilbert, just north of Ames.  The public is welcome to visit the planting on weekdays from 8 a.m. to 4 p.m.  Call the Horticulture Research Farm at (515) 232-1978, or Mark Gleason at (515) 294-0579, for directions to the trial site. 

As the trial progresses, we will post our observations on an ISU Extension Web site, along with a map of the trial site, photos of the trees, and contacts for nurseries where they can be purchased.  I’ll also share results in this column from time to time.

It’s heartening that we finally have some hopeful prospects for revival of elms in our communities. Stay tuned!

For more information about “Dutch Elm Disease and Disease-Resistant Elms,” (SUL 4) see Iowa State University Bulletin SUL 4, available for $3 at ISU Extension County Offices or through ISU Extension Distribution online store at www.extension.iastate.edu/store/ or by calling (515) 294-5247.


Contacts :

Mark Gleason, Plant Pathology, (515) 294-0579, mgleason@iastate.edu

Jean McGuire, Continuing Education and Communication Services, (515) 294-7033, jmcguire@iastate.edu