90% of butternut trees have been infected by butternut canker, a fungal disease, throughout their native range which stretches from Georgia to Minnesota to New Brunswick Canada.
The disease has been spreading rapidly and has been killing off more and more butternut. Dr. Dale Bergdahl, a retired forestry professor at the University of Vermont, was the first to find the canker in Vermont in the fall of 1983. SInce that time half of the butternuts in Vermont have been killed.
Dr. Bergdahl and his colleagues have tracked the spread of the disease by setting up 18 permanent research plots in Vermont between 1993 and 1996. They measured, tagged and evaluated the health of 1,269 butternuts and logged their Global Positioning System coordinates. They found that by 1996 92 percent of the trees were infected with the fungus, Sirococcus clavigignenti-juglandacearum, and that 12 percent had died as a result. By 2002 the percentage of infected trees increased to 96 percent and 41 percent of the trees were dead.
In 2003 and 2004, Dr. Bergdahl and his colleagues set up an additional 24 plots and evaluated another 1,054 butternuts in Vermont. Every butternut evaluated was infected with the fungus, and half were dead. There was almost no regeneration among the butternut stands, and the few young trees found were infected. Dr. Bergdahl predicts that by 2011, 85% of the butternuts in Vermont will have been killed.
It is believed that the spores of the fungus are spread through rain, wind and insects. Dr. Bergdahl and his associates have found that seventeen species of beetles closely associated with butternut can carry the spores. One beetle can carry up to 1.6 million spores. Only one spore is needed to cause infection. The fungus can also be carried on the nut causing some trees to be infected before they begin to grow.
In October 2006, 40 scientists and foresters, including Dr. Bergdahl, met in Niagara Falls, Ontario, for the Butternut Canker Research Symposium. It was a first step which allowed scientists to share research. At this time there is no known treatment for butternut canker, so efforts are being focused on finding and protecting resistant trees. This is not easy because the trees that appear resistent may not be genetically pure since butternuts can breed with other trees, such as the Japanese walnut.
Some states and Canada have taken measures to protect the butternut. Since 1992 there has been a moratorium in Minnesota on the harvest of healthy butternut trees from state-owned lands. The US Forest Service has begun a program in Wisconsin to preserve disease-free selections by grafting butternut scion onto black walnut roots to produce seeds for restoration projects. Canada's Species at Risk Act lists butternuts as endangered. As a result, Tannis Beardmore, a researcher with the Canadian Forest Service, is keeping fungus-free butternut seeds in frozen storage.
Dr. Bergdahl noted that there was no organization to advocate for the butternut tree and has said he is interested in starting one that would be focused on protecting butternuts. He can be reached at Dale.Bergdahl@uvm.edu.
Dr. Bergdahl suggests that butternut lovers who want to increase the butternut population plant nuts in open areas covered by a screen to keep squirrels away.
