By Ta’i H. Roulston
Butternut trunk showing the flattened bark that often makes a diamond pattern and the dark colored wounding resulting from butternut canker disease.
It is a common story, move diseases to new continents and the disease finds new hosts and destroys them. Think chestnut blight and Dutch elm disease, and now beech leaf disease. It can also happen in reverse—bring foreign trees here and watch them get attacked by local diseases. When European hazelnut was brought to the U.S. for orchard plantings, it was attacked by eastern filbert blight, an endemic but non-fatal disease of native wild hazelnuts.
In the eastern U.S., one of the most prominent but little-known examples of native tree decline by exotic disease is butternut canker, a fungal disease that devastates wild butternut trees (a.k.a., white walnut, Juglans cinerea). It has wiped out 50-90% of butternut trees across its range since the 1960s. When you find the tree, you usually find symptoms of the disease –longitudinal dark fissures in the bark that eventually girdle and kill the tree. When you find several trees together, all diseased and dying with no seedlings coming up, it feels like you’re walking through a time-lapse of extinction.
The loss of butternut would leave a substantial ecological and cultural hole in the landscape. Ecologically, the large, nutrient-rich seeds provide abundant food for wildlife. Culturally, the trees have provided food, medicine, and workable wood for indigenous peoples for millennia. The nuts are one of the 46 traditional foods served at Cherokee traditional feasts in the southern Appalachians. The earliest European settlement in North America, that of the Norse in Newfoundland at L’Anse aux Meadows in the 11th century, contains archaeological remains of butternut seeds and wood, indicating early recognition of the value of butternut by the first Europeans. During the Civil War, butternut seed husks were often used to dye Confederate uniforms. The seeds are still collected and eaten today and the wood is valued for furniture and carvings because of its workability, even though large pieces are hard to find.
Leaf of butternut (J. cinerea)
Nut of a butternut tree
Despite its decline, the tree is still regularly encountered the entire length of Virginia, from the Piedmont to the western border. It is most commonly found along rivers, but can be found in fields, roadsides, or ridgetops, wherever light is plentiful. The largest tree in the state is in Loudoun County at 65 feet tall with a trunk nearly 6 feet in diameter. Other large ones are scattered about, and, remarkably, some of them appear healthy. We are on a hunt for these large healthy trees! Propagating trees that will survive in a landscape full of disease requires finding trees that are resistant to the disease. There is no cure for butternut canker, but there still may be resistant trees out there to find. For several decades, research programs at Purdue University, USDA, The Morton Arboretum and the Canadian Forestry Service have been studying butternuts and butternut canker, trying to find resistant trees for a future breeding program. No trees have been found to be completely resistant, but some lineages appear to have moderate levels of resistance that could contribute to breeding programs. Virginia has been ignored in most studies, despite having a large land area where the trees naturally occur. So we are undertaking a large search for trees across the state and if you know where to find them, please help!
How can you help? If you know where to find butternut trees please contact me or my graduate student Mia Murray. We are looking to get exact tree locations, photos of trees to confirm tree identification and disease status, and leaf samples for genetic analysis. The genetic analysis is to confirm that the tree is not a butternut x Japanese walnut hybrid, which sometimes grows wild.
Tree falling apart from butternut canker disease, close to death.
There are three ways to help:
1) If the tree is on your land, take photos and a leaf sample and send them to us (we’ll tell you how and provide packaging);
2) If the tree is on your land but you can’t reach any leaves, send us the photos and we’ll come to collect the leaf by slingshotting a line over the lowest branch and shaking off a leaf; or
3) If the leaf is on public land, take a photo and we’ll get a permit for collecting the leaf sample and then come to collect it.
After we get genetic samples back, we will choose the largest, healthiest looking trees to visit in the fall for collecting fruit samples to propagate. We’ll be propagating the seeds at the State Arboretum of Virginia in Boyce, Virginia and assessing resistance over many years. While we are mainly collecting seeds from healthy trees, we want to know where any trees are in the state to assess the extent of disease spread and tree survival over time.
Everything starts with simply reaching out to us at uvabutternuts@virginia.edu. We’ll provide all the details about getting involved, how to take the photographs and leaf samples, and anything else you want to know about the project. Thank you for helping preserve butternut for future generations.