Butternut blues – US butternut tree, endangered species – Forest Health

Butternut blues – US butternut tree, endangered species – Forest Health – Cover Story

Rich Patterson

More threatened than even the American chestnut, the “white walnut” may be headed for the Endangered Species list.

One morning last fall, a middle-aged woman entered my office at Iowa’s Indian Creek Nature center.

“When I was a young girl,” she said, “my father took me out to gather butternuts. We’d crack them at home by the woodstove. They were wonderful, and I want take my own kids out to gather some. We went back to the family farm, but I couldn’t find any. Do you know where we might gather a few?”

As the Center’s director, I try to help people solve their nature problems, and I knew we had some large butternuts up near our north property line. I told her I’d gladly abandon paperwork for a while and walk up there to inspect the nut crop.

A half hour later, we stood at the base of a wide-spreading butternut nestled amid white oaks overlooking the Red Cedar River. Although squirrels had made off with most of the crop, we gathered enough for her to make a couple of plates of cookies for her kids.

As we walked back to her car, we passed other, scattered butternut trees, and gloom descended on us. Although the husky tree that yielded our nuts appeared healthy, all the others we passed were loaded with a disease called butternut canker. Many were dead, standing or toppled; others were obviously fighting a losing battle.

“That’s why you’re not finding butternuts,” I said. “The healthy tree where we found the nuts is the only one I know of around here.”

Tragedy has befallen the butternut. “It is more threatened than even the American chestnut,” said Mike Ostry, a U.S. Forest Service research plant pathologist. “In fact, it may be the first tree I’m aware of that’s being considered for addition to the Endangered Species List.”

Butternut has declined so steeply that Minnesota has banned cutting it on state lands. At least two-thirds of Wisconsin’s butternuts have visible cankers, and death awaits them.

As the accompanying articles clearly show, tree epidemics aren’t unprecedented. Unfortunately, butternut canker (actually a fungus) appears to be doing a more thorough job of eliminating its host than even the chestnut and elm diseases.

“There’s an awful lot we don’t know about butternut canker,” said Ned Tisserat, a Kansas plant pathologist. Tisserat studied the disease for his PhD dissertation at the University of Wisconsin.

A major problem in studying the butternut canker disease is the nature of the tree itself. The butternut, Juglans cinerea, is not and never has been very common. It tends to be solitary and rarely forms groves. Butternuts are scattered all over their range, which takes in a huge swath of the continent, from New England southward to northern Alabama and westward into Iowa. They are probably most common in Wisconsin.

As a general rule, the butternut tolerates colder climates and rockier soil than its close relative, the black walnut. In fact, many people call butternut the white walnut, a reference to its wood of light weight and color that has excellent working qualities, beautiful grain, and a natural sheen.

The tree produces a nut similar to the black walnut, but it’s oblong instead of round and is even tastier and oilier. Also like the walnuts, the nut husk and bark contain a powerful dye that stains the hands and can be used to color clothing. Generally, the tree is better known for its nuts than its wood.

Unlike black walnuts, butternut trees are short-lived and medium to small in stature. An old specimen may span three-quarters of a century. Rarely do they reach over 60 feet high, and most are under two feet in diameter. Like walnuts, butternuts love sunlight and usually die if shaded by faster-growing trees.

Butternut’s habit of living in isolation makes the spread of the canker disease baffling. “Usually epidemics are fueled by high densities of a species,” said Ostry. That makes it easy for disease to rapidly spread from tree to tree, as with the Dutch elm, chestnut, and dogwood diseases.

“You would think that scattered butternut trees would be protected by their isolation, but they are catching the canker disease everywhere,” Ostry said.

Butternut canker, Sirococcus clavigignenti-juglandacearum, first identified in 1967, is now found throughout the tree’s range. It is not known if the canker was introduced from overseas or if it’s an old disease that mutated into a virulent form.

Ostry believes the canker spread to the Midwest from the East. Tisserat’s research indicated it may have moved into Wisconsin and Minnesota from an outbreak near Dubuque, Iowa. At any rate, too little is known about the disease, how it moves so effectively across vast distances, and how to protect healthy trees.

Butternut canker produces spores that enter healthy trees through a leaf scar or bark injury. Infected trees form cankers, usually starting on lower branches. These spread to the trunk, where large cankers form. Unlike many other pathogens, the fungus doesn’t produce a toxin that kills the tree. Rather, trees produce so many cankers that they girdle themselves and choke to death. Death may occur within a few years after the tree is first infected.

To compound the butternut’s woes, deer love to rub their newly formed antlers on the smooth bark of young trees in autumn. Large bark wounds result, and canker seems to quickly enter.

The butternut fungus has traits that set it apart from other, better-known tree diseases. When the chestnut blight infects trees, for example, it kills above-ground growth but not roots. Some chestnut roots have sent up sprouts for decades, keeping the genetic basis of the tree alive. Also, many chestnuts were planted beyond the tree’s natural range before the blight hit. They remain healthy. Dutch elm disease spread across the country relatively slowly, allowing researchers time to study the disease and search for solutions.

The butternut is not so fortunate–the canker disease is striking trees of all sizes everywhere. Once infected, a tree dies, taking all genetic memory with it. There is nothing an owner can do to protect or cure his tree. The butternut has another strike against it. Unlike the chestnut, elm, and dogwood, it simply isn’t familiar to most Americans. It has never been an urban tree–few city people can recognize one. Many have never even heard of it. The decline of the butternut is being mourned mostly by foresters and Americans with rural roots, like the woman who came to me seeking nuts.

Because the butternut is neither a tree of the city nor an important lumber species, it was a while before anyone took serious notice of its decline. And although a few researchers, like Ostry, are scrambling to understand the disease and find solutions, the epidemic is leveling butternuts so rapidly that they could pass into oblivion before a cure is found.

Trees with natural resistance may be the best hope for the American butternut. “We don’t know if resistant trees even exist,” Ostry says, but he is attempting to locate healthy butternuts in order to obtain scion wood. Unfortunately, woodland owners sometimes harvest all their butternuts as soon as the disease is discovered on the property. In the process, they may cut down a potentially resistant tree.

I fervently hope that some resistant trees remain out there in the woods, so that future generations of American children will be able to enjoy delicious butternut cookies and the other benefits of this unique tree.


Researcher Mike Ostry would like to hear from anyone owning healthy butternuts that have the following criteria:

* The tree should be near canker-ridden trees so it can be assumed that it has had heavy exposure to the disease.

* Tree appears to be free of cankers or has successfully overgrown them.

* Tree has a diameter at breast height of at least 10 inches.

* Owner will allow researchers to collect scion wood and nuts for several years.

If you know of a butternut that fits these criteria, please contact Michael E. Ostry, Research Plant Pathologist, U.S. Forest Service, 1992 Folwell Ave., St. Paul, MN 55108.

Rich Patterson is director of the Indian Creek Nature Center near Cedar Rapids, Iowa, and a freelance writer.

COPYRIGHT 1993 American Forests

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