Nightmare on Elm Trees

A Publication ofthe American Horticultural Society Volume 69, Number 7 • J uly 1990 $1.50 News Edition Nightmare on Elm Trees Can we ever hope for a rebirth of this beloved native tree? trees go, its flowers are insignificant, its fall color oflittle note, its bark pretty blah. It's susceptible to an endless list of iseases; insects can't get enough of it. ABut what an easily grown and shapely landscape tree it was! Planted in rows along so many American streets, its unique spreading vase shape turned them into veritable cathedrals. But the rows are largely gone now, victim to the Dutch elm disease that was first recognized in the 1930s. Can those of us who grew up under elms hope to go home again? While some scientists continue to look for a cure for Dutch elm disease, breeders are seeking a cultivar of Ulmus americana that's impervious to the disease, or an Asian counterpart that will serve as a substitute. There has been some progress, and some frustrations, on both fronts. Fighting the Fungus John Hansel says he's like a lot of other people who grew up under elms and was incredulous at seeing them begin to die by the hundreds. In 1967, Hansel, the owner of a New Hampshire manufacturing firm, established the Elm Research Institute to raise money for research that might save the elm, and at first, a good deal of that money went toward finding a treatment that would stop or prevent the fungus, Ceratocystis ulmi, that causes Dutch elm disease. Because the fungus is spread by beetles, DDT served as an effective treatment until its use was halted for ecological reasons in the 1960s. Nothing as cheap or powerful has been found since, despite efforts in many directions. Says Hansel: ''We got into a lot of In This Issue biological experiments, including using predators such as wasps and using a Return of the Elm 1 Regional Notes ..... 12 pheromone for trapping beetles. But Members' Forum 5 Williamsburg Symposium 15 traps are totally impractical for insects so tiny that they're like a cloud of dust." Outdoor Lighting 6 AHS Bulletin Board 16 ERI-funded research led to the development of a procedure in which a Gardener's Q&A 8 Gardener's Bookshelf 18 fungicide, benzimidazole carbamate salt (sold as Lignasan BLP), was Making a Difference .10 Gardener's Dateline 20 injected into the tree just below No Immune American American ground level. A 1986 study reported that injecting elms with the fungicide Researchers who have tried to breed a Horticultural Society saved about 25 percent of all of those disease-resistant American elm have with Dutch elm symptoms, and that known the deck was stacked against The American Horticultural Society seeks thirty-three percent of those with only them from the start. The odds are to promote and recognize excellence minimal symptoms survived. Similar against just happening upon a in horticulture across America. results were obtained with injections naturally resistant selection, and the of Arbotect, a derivative ofbenomyl. American elm can't be crossed with OFFICERS 1990-1991 Encouraged by the results, the Elm more resistant Asian elms because Mr. George C. Ball Jr., West Chicago, IL Research Institute organized what it they have differing numbers of President called a "Conscientious Injector" chromosomes. Occasionally a selection Mrs. Helen FulcherWaiutes, MountVemon, VA program of volunteers whose goal was will look promising, but susceptibility First Vice President injecting 100,000 elms across the to Dutch elm disease is usually not Mr. Richard C. Angino, Harrisburg, PA country. Institute literature says the apparent until the tree is mature; also Second Vice President Mr. Elvin McDonald, Brooklyn, NY treatment can save 98 percent oftrees in doubt until maturity is whether the Secretary on which it was used. But Hensel says tree will have the sought-after vase Mrs. Jane N. Scarff, New Carlisle, OH this is true only when the trees are shape. Michael Dirr, in his Manual of Treasurer completely disease-free, and notes that Woody Landscape Plants, observes that Mrs. carolyn Marsh Lindsay, R6cMester, NY early signs may be impossible to there are actually three distinct shapes Immediate Past President detect. "It's like a cancer." among the American elm, including a Treatment may also be hampered by narrow form and an "oak form" in BOARD OF DIRECTORS a number of environmental factors. which the branches are widely Dr. William E. Barrick, Pine Mountain, GA The elm's own vascular system, which spreading and less arching. Barring Dr. Sherran Blair, Columbus, OH Mrs. Mary Katherine Blount, Hansel compares to a corkscrew, tends Montgomery, AL to slow uptake ofthe fungicide. Mrs. Sarah Boasberg, Washington, DC Discouraged by nature's apparent Dr. Henry Marc Cathey, Washington, DC efforts to thwart humans' best Where Did It Mr. Russell B. Clark, Boston, MA intentions, the institute is now putting Mrs. Ann Lyon Crammond, Atlanta, GA proportionately more of its resources Come From? Mrs. Beverley White Dunn, into breeding than in finding a cure. Birmingham, AL Meanwhile, in the late 1970s, a The Dutch got a bad rap when they Mr. K. Albert Ebinger, Boxford, MA Montana research group began pursuing Mr. Gerald T. Halpin, Alexandria, VA were stuck with the name for the the idea of finding a natural bacterium Mrs. Julia Hobart, Troy, OH devastating elm tree disease, since that would ;fight off the Dutch elm Dr. Joseph E. Howland, Reno, NV in fact, they have done some of the disease fungus. They, as well as R.J. Mr. David M. Lilly, Saint Paul, MN most useful research directed at Scheffer of Holland, discovered that a Mr. Everitt Miller, Kennett Square, PA finding a cure. Gary Strobel, bacterium called Pseudomonas syringae Mrs. Flavia Redelmeier, professor of plant pathology with Toronto, Ontario, Canada would kill the fungus. Mr. Andre Viette, Fishersville, VA While Scheffer carried out field tests Montana State University, writing with Richard Gray in a recent Mrs. Jean Verity Woodhull, Dayt0n, OH in Holland on some 7,000 European American Nurseryman, notes a elms; Americans Gary Strobel, Steve theory that the disease o~iginated EXECUTIVE DIRECTOR Lam, and Brenda Lam became curious in ASia, and was brought to Europe Mr. Frank L. Robinson about how the bacterium killed the on the Trans-Siberian Railroad fungus. They created a mutant strain during World War I. The fact that AMERICAN HORTICULTURIST ofthe fungus that could be tracked as most Asian elms are immune to the it moved through an elm, and began a disease, while European and EDITOR: Kathleen Fisher field test to see ifit would work on ASSISTANT EDITOR: Mary Beth Wiesner American natives are susceptible, mature elms as well as seedlings. But EDITORIAL ASSISTANT: Martha Palermo "dovetails nicely with this theory," they made a procedural error. The MEMBERSHIP DIRECTOR: they write. It was a Dutch botanist, Environmental Protection Agency Kathleen B. Amberger Marie Beatrice Schwarz, who requires review of all genetically ADVERTISING: American HorticuHural discovered the cause of the tree Society Advertising Department, 80 South altered micro-organisms released into loss; about half of Holland's elms Early Street, Alexandria, Virginia 22304. the environment. Strobel and his Phone (703) 823-6966. colleagues thought it wasn't necessary were destroyed. The disease is spread from tree in this case, since the same strain had Address all editorial correspondence to: The Editor, , to tree by elm bark beetles, who American Horticulturist, American Horticultural been released years earlier. But a Society, 7931 East Boulevard Drive, Alexandria, mate on the trees before the local newspaper drew attention to the Virginia 22308. AMERICAN HORTICULTURIST, ISSN females bore into the tree to lay 0096-4417, is publishes by the American Horticultural work, the experiment received nega their eggs. The larvae and new Society, 7931 East Boulevard Drive, Alexandria, Virginia tive publicity nationwide, and Strobel 22308, (703) 768-5700, and is issued six times a year as adults further enlarge the tunnels. a magazine and six times a year as a news edition. The cut down and burned his 14 inoculated The fungus produces toxins and American Horticultural Society is a nonprofit organization elms. It was a serious setback, he says, devoted to excellence in horticulture. Botanical nomen· deposits that clog the trees' but his group is continuing to study clature in AMERICAN HORTICULl'URIST is based on vascular system, cutting off the HORTUS THIRD. National membership dues are $35; the substances that the bacteria uses two years are $60. Foreign dues are $45. $12 of dues are flow of water and nutrients. The deSignated for AMERICAN HORTICULTURIST. to fight the fungus; work similar to disease apparently was brought to Copyright © 1990 by the American Horticultural SOCiety. Scheffer's is being carried out by Chris the United States in elm logs Second·class postage paid at Alexandria, Virginia ans at Murdock of the University of Maine in additional mailing offices. Postmaster: Please send Form imported for use as veneer 3579 to AMERICAN HORTICULTURIST, 7931 East Oronco, Strobel reported in a recent because of their interesting burls. Boulevard Drive, Alexandria, Virginia 22308. issue of American Nurseryman. 2 + American Horticulturist • July 1990 the extremely slim possibility of a naturally occurring mutation, the most likely source of a Dutch-elm-immune American lies within the still young field of genetic engineering. For now, the most promising American elms available to the public are the American Liberty elms, developed by University of Wisconsin scientists with the backing of the Elm Research Institute. Researchers Eugene Smalley and Raymond Guries describe these elms as "genotypically diverse multiclones having similar phenotypes," which means they look almost identical but aren't quite the same genetically.

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