From the City of Eugene
Eugene's urban forest is facing a very serious threat from a new disease called Thousand Cankers Disease that is killing black walnut trees in eight western states.
Laboratory analysis at the Plant Clinic at Oregon State University (OSU) confirmed the large walnut on Madison Street next to Gray's Garden Center to be the first known case in Eugene found to have the disease.
The disease has probably been present in Eugene for the last few years, and it has already been found in every county in the Willamette Valley, according to Dr. Jay Pscheidt, OSU Extension Plant Pathology Specialist.
Thousand Cankers Disease is caused by a newly-discovered fungus (Geosmithia morbida) that is carried to trees by the tiny walnut twig beetle. The fungus kills areas of bark throughout the tree. Cankers eventually grow together and girdle limbs and the trunk so nutrients can no longer move in the tree.
Trees in the Willamette Valley typically die within two to five years after showing their first symptoms of summer leaf yellowing and branch dieback. Currently, there are no known insecticides or fungicides that control the beetle or disease.
"The City is working with Oregon State University, Lane County Extension Farms, and Gardens Program, and local arborists and governmental agencies to figure out the best way for us to act responsibly in limiting the spread of this disease when we handle affected trees," says Mark Snyder, City of Eugene urban forester. "Since there is no known cure at this time, community members should work with their tree care professional to determine whether or not a tree they are concerned about is a black walnut tree and if it is infected (many Oregon walnuts are hybrids and are less susceptible, as is the English walnut).
Walnut heartwood (found only in tree trunks) may be able to be processed at custom sawmills to help offset the cost of removal. Since the value of the trunk wood does not diminish as the tree dies, there is no hurry to remove a tree before it dies or has substantial branch death. Pruning out the dead wood may delay death for a few years, but it has not been shown to save trees. Be sure not to transport firewood, though, as this will spread the disease. Two 18-inch pieces of firewood in Colorado were found to still be infested with over 23,000 beetles one year after cutting."
Community members who have questions can contact Lane County Extension Service Farms and Gardens Program, 783 Grant Street, at 541-344-0265 (Master Gardener hotline). If there is a tree in the street right-of-way (lawn strip between the curb and sidewalk) that a community member suspects may be infected, they can contact the City of Eugene Parks and Open Space Division at 541-682-4800 to request an inspection.