Townsend and his colleagues tested thousands and thousands of seedlings. In the mid-1970s, Townsend and Schreiber decided to test some wild elms that had survived the epidemic to determine if one tree held the secret to resistance. Townsend laughs recalling the patience of his wife, Anne, and sons, Jeffrey and David, as he stopped the car on family outings to take extensive notes on a particular elm tree left standing. “It was really a long shot to seek out survivor trees in the wild,” Townsend says. “We didn’t know if they were just lucky or truly resistant.”

Still, Townsend and his colleagues traveled Ohio roads to visit healthy American elms growing in farmers’ fields, in cities, and along highways. In the late 1970s, Townsend spotted a healthy elm growing along I-70 near Springfield, Ohio, a suburb of Dayton. He noted its location and kept observing its health over several years. “It was a huge tree that looked nice, but later had a lot of problems due to flooding and other things,” says Larry Schreiber, now retired as a USDA plant pathologist and living in Delaware, Ohio. “It was kind of a miserable-looking tree toward the end.” But, in spite of the tree’s eventual fate, the team took a cutting in the spring of 1980. They propagated it by scraping the twig near its base and dipping the wound in growth hormones that encouraged roots to sprout. Once roots appeared, the cutting was nurtured in a greenhouse for six weeks, switched to a pot, and eventually transplanted to a test plot.

As his elm cuttings become old enough for testing, Townsend tries very hard to kill them. When the trees reach four years of growth, he injects a murky cocktail containing the Dutch elm disease fungus into the base of the tree. “We use a very severe dose of 3 million spores per milliliter,” Townsend says. “In contrast, an elm bark beetle carries 10 to 100 spores and introduces the fungus into the top of the tree.” Some trees are injected at different times of the year to see if seasonality is a factor for disease resistance.

Infected trees die from a process similar to hardening of the arteries. The fungus travels through the tree’s xylem, the circulatory system that carries water and nutrients from the roots to the branches. Over time, the fungus causes protrusions in the xylem, which cut off the flow of water and nutrients. Most elms die within two or three years after infection.

Townsend and horticulturist Susan Bentz inspect seedlings in one of the research greenhouses at the U.S. National Arboretum tree-breeding facility in Glenn Dale, Maryland.

Sixteen years ago, when Townsend was transferred to the USDA’s National Arboretum facility in Maryland, 10 disease-tolerant elms had been identified. Now, nearly every day, less than two miles from the Beltway, Townsend turns off a jammed street outside Greenbelt, Maryland, and enters a USDA facility that time seems to have forgotten. Nestled amid trees of all sizes, shapes, and species, their small building complex is an oasis of trees in a sea of malls, government offices, and housing developments. Townsend and horticulturist Susan Bentz work in what can charitably be called spartan conditions. The offices and greenhouses look like the back room of a hardware store. But beyond the buildings lie fields of elms, maples, hemlocks, and other trees—all in various stages of testing.

In a final series of tests at Glenn Dale, offspring from the Springfield, Ohio, elm proved remarkably tolerant of the disease. At the same time, offspring from another elm seedling derived from a Nebraska seed source proved to be a disease-tolerant clone. The elm cultivar grown from the seedling clone was named Valley Forge, and the elm grown from the Ohio tree was dubbed New Harmony.

So far, many nurseries and towns have expressed interest in trying out the arboretum’s elm varieties. Penn State has 12 of his trees growing in their replacement nursery, although the elms are not available at retail nurseries yet. In 1996, a Valley Forge elm was planted on the grounds of the U.S. Capitol. “Denny is restoring part of our heritage,” says Ohio State urban forest scientist T. Davis Sydnor. “We get to enjoy the same shade and arching branches that our fathers and grandfathers enjoyed. If I had to predict, I’d say that by 2010, the elm will be a commonly planted tree again.”

Townsend sees his work on the American elm as an ongoing project that other scientists will continue long after he retires beneath the shade of his own backyard trees. He would like to see the discovery of an American elm truly
resistant to Dutch elm disease, and he remains optimistic that researchers will soon unlock how the disease functions within the tree. “Propagating disease-tolerant elms is not the end of this research,” he says. “It is only the beginning.”